Prepreg, intermediate material for forming frp, and method for production thereof and method for production of fiber-reinforced composite material

ABSTRACT

An FRP is produced using a prepreg comprising reinforcing fiber, a sheet-like reinforcing fiber substrate containing reinforcing fiber, and a matrix resin, wherein the matrix resin is impregnated into the sheet-like reinforcing fiber substrate and also covers one surface of the sheet-like reinforcing fiber substrate, and the matrix resin impregnation ratio is within a range of 35% to 95%; a prepreg comprising reinforcing fiber, a sheet-like reinforcing fiber substrate containing reinforcing fiber, and a matrix resin, wherein the matrix resin exists on both surfaces of the sheet-like reinforcing fiber substrate, and the portion inside the sheet-like reinforcing fiber substrate into which the matrix resin has not been impregnated is continuous; or a prepreg comprising reinforcing fiber, a sheet-like reinforcing fiber substrate containing reinforcing fiber, and a matrix resin, wherein at least one surface exhibits a sea-and-island-type pattern comprising resin-impregnated portions (island portions) where the matrix resin is present at the surface and fiber portions (sea portions) where the matrix resin is not present at the surface, the surface coverage ratio of the matrix resin on those surfaces with said a sea-and-island-type pattern is within a range of 3% to 80%, and the weave intersection coverage ratio for the island portions, represented by a formula (1) shown below, is at least 40%, displays excellent external appearance, with no internal voids or surface pinholes, even when molded is conducted using only vacuum pressure. 
       Island portions weave intersection coverage ratio (%)=( T/Y )×100  (1) 
     (wherein, T represents a number of island portions that cover weave intersections, and Y represents a number of weave intersections within said reinforcing fiber woven fabric on said surface with said sea-and-island-type pattern).

TECHNICAL FIELD

The present invention relates to a prepreg that functions as anintermediate material for FRP molding.

BACKGROUND ART

Fiber-reinforced composite materials (hereafter also abbreviated as FRP)are lightweight, while offering good strength and high rigidity, and areconsequently widely used in a variety of applications from sports andleisure through to industrial applications such as vehicles andaircraft. In recent years, with the fall in the cost of carbon fiber,the use of carbon fiber reinforced composite materials (hereafterabbreviated as CFRP), which are even more lightweight and offer evenhigher levels of strength and rigidity, within industrial applicationshas also become more widespread.

Amongst these potential industrial applications, CFRPs used forstructural members within train bodies and aircraft frames are typicallyproduced by autoclave molding, using an intermediate material known as aprepreg. The reason for this preference is that by conducting themolding under high pressure using an autoclave, not only can theoccurrence of voids within the molded product be reduced, enabling thestrength of the molded product to meet expectations, but the occurrenceof surface pinholes can also be suppressed, enabling the production of amolded product with a favorable external appearance.

However, autoclave facilities are extremely expensive, which not onlyacts as a large barrier to new entrants, but also means that onceautoclave facilities are purchased, the size of the molded products isrestricted by the size of the autoclave, meaning the production oflarger products is effectively impossible.

In order to avoid these problems, the development of autoclave-free, lowcost molding is also progressing, and representative examples of suchmolding include oven molding under either vacuum conditions or normalatmospheric conditions (also known as vacuum bag molding). Oven moldingdoes not require the application of pressure, meaning the molding can beconducted without the need for a proper pressure-resistant vessel suchas an autoclave, and molding can be conducted simply with a furnace forraising the temperature. Molding can also be conducted with a simpledevice comprising an adiabatic board and a hot air heater. However,because these processes do not involve the application of pressure,residual voids tend to remain within the molded product, the strength ofthe molded product is inferior to that of a molded product produced inan autoclave, and pinhole formation is also a problem.

In recent years, a variety of measures for overcoming these problemshave been proposed. For example, WO 00/27632 discloses technologyrelating to materials comprising a resin layer and a reinforcing fiberlayer, which display minimal void generation, and enable the productionof molded products with extremely clean surfaces, even when used withoven molding. However, with this technology, almost all of the resin isimpregnated during molding, and depending on the molding conditions,portions of the resin that display unsatisfactory impregnation canoccur, leading to the occurrence of internal voids and surface pinholes.Furthermore, because the surface is almost free from resin and isextremely dry, workability problems such as difficulty in bonding theproduct to the molding die can also be a concern.

DISCLOSURE OF INVENTION

An object of the present invention is to provide an intermediatematerial, which retains the level of workability associated withconventional prepregs, while enabling the production of a FRP with nointernal voids or surface pinholes, but with excellent externalappearance, using molding at only vacuum pressure, without the use of anautoclave.

A first aspect of the present invention is a prepreg comprisingreinforcing fiber, a sheet-like reinforcing fiber substrate containingreinforcing fiber, and a matrix resin, wherein the matrix resin isimpregnated into the sheet-like reinforcing fiber substrate and alsocovers one surface of the sheet-like reinforcing fiber substrate, andthe matrix resin impregnation ratio is within a range of 35% to 95%.

Furthermore, a second aspect of the present invention is a prepregcomprising a matrix resin, and a sheet-like reinforcing fiber substrate,wherein the prepreg comprises reinforcing fiber, a sheet-likereinforcing fiber substrate containing reinforcing fiber, and a matrixresin, wherein the matrix resin exists on both surfaces of thesheet-like reinforcing fiber substrate, and the portion inside thesheet-like reinforcing fiber substrate into which the matrix resin hasnot been impregnated is continuous.

Furthermore, a third aspect of the present invention is a prepregcomprising a sheet-like reinforcing fiber substrate formed from areinforcing fiber woven fabric, and a matrix resin, wherein at least onesurface displays a sea-and-island-type pattern comprisingresin-impregnated portions (island portions) where the matrix resin ispresent at the surface and fiber portions (sea portions) where thematrix resin is not present at the surface, the surface coverage ratioof the matrix resin on surfaces with the sea-and-island-type pattern iswithin a range of 3% to 80%, and the weave intersection coverage ratiofor the island portions, as represented by a formula (1) below, is atleast 40%.

Island portions weave intersection coverage ratio (%)=(T/Y)×100  (1)

(wherein, T represents the number of island portions that cover weaveintersections, and Y represents the total number of weave intersectionsof the reinforcing fiber fabric on the surface with thesea-and-island-type pattern).

Furthermore, a fourth aspect of the present invention is an intermediatematerial for FRP molding comprising a prepreg containing reinforcingfiber and a matrix resin, and a substrate containing essentially noimpregnated thermosetting resin composition, which is provided on atleast one side of the prepreg, wherein the ratio (B)/(A) between thethickness (A) of the prepreg, and the thickness (B) of the substrate iswithin a range of 0.1 to 2.5.

Using the aspects described above, the level of workability associatedwith conventional prepregs can be retained, while FRP with no internalvoids or surface pinholes, but with excellent external appearance can beproduced using molding at only vacuum pressure, without the use of anautoclave.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a prepreg that uses a sheet withthe fibers aligned unidirectionally as the sheet-like reinforcing fibersubstrate, viewed in a cross section cut perpendicularly to thedirection of the fibers.

FIG. 2 is a schematic illustration of a prepreg that uses a plain weavefabric as the sheet-like reinforcing fiber substrate, viewed in a crosssection cut perpendicularly to the warp.

FIG. 3 is a schematic illustration showing one example of a prepregaccording to a second embodiment of the present invention.

FIG. 4 is a schematic illustration of a prepreg of a comparativeexample, wherein the matrix resin has been supplied from one surface.

FIG. 5 is a schematic illustration of a prepreg of another comparativeexample, wherein although the matrix resin has been supplied from bothsides, portions that have not been impregnated with the matrix resin donot exist in a continuous state.

FIG. 6 is a schematic illustration showing the surface of a prepregaccording to a third embodiment of the present invention.

FIG. 7 is a schematic illustration of a comparative example, showing thesurface of a prepreg wherein a island portions weave intersectioncoverage ratio is low.

FIG. 8 is an example of a graph showing the results of measuring thedynamic modulus of elasticity of a matrix resin, as well as a method ofdetermining the value of Tg from such a graph.

BEST MODE FOR CARRYING OUT THE INVENTION

As follows is a description of the composition of the present invention.

A first embodiment of the present invention is a prepreg comprising asheet-like reinforcing fiber substrate formed from reinforcing fiberthat has been impregnated with a matrix resin, wherein only one surfaceof the sheet-like reinforcing fiber substrate is covered with the matrixresin, and the resin impregnation ratio is within a range of 35% to 95%.There are no particular restrictions on the fiber used in the sheet-likereinforcing fiber substrate used within this first embodiment of thepresent invention, and examples of suitable fibers include carbon fiber,glass fiber, aramid fiber, high-strength polyethylene fiber, boronfiber, and steel fiber. Carbon fiber is preferred as it results in morefavorable properties for the generated FRP, particularly in terms ofreduced weight and favorable mechanical properties such as high strengthand high rigidity.

Furthermore, there are also no particular restrictions on the form ofthe sheet-like reinforcing fiber substrate used in the prepreg of thisfirst embodiment, and suitable examples include plain weave fabric,twill fabric, satin weave fabric, stitched sheets such as non-crimpedfabric (NCF) wherein fiber bunches are layered, either unidirectionallyor at various angles, and then stitched to prevent the layers comingapart, as well as non-woven fabric, mats, and unidirectional materialsin which a bundle of reinforcing fibers is aligned unidirectionally. Ofthese, woven fabrics and stitched sheets, which offer superior levels ofhandling, are preferred.

Furthermore, there are also no particular restrictions on the matrixresin used in the prepreg of the first embodiment, and eitherthermosetting resins or thermoplastic resins can be used, although fromthe viewpoints of the handling of the prepreg, such as the tack anddrape characteristics, and the moldability, thermosetting resins arepreferred. Examples of suitable thermosetting resins include epoxyresins, phenol resins, vinyl ester resins, unsaturated polyester resins,bismaleimide resins, BT resins, cyanate ester resins, and benzoxazineresins, although in terms of handling properties and the properties ofthe resulting cured product, epoxy resins, bismaleimide resins, BTresins, and cyanate ester resins are preferred, and of these, epoxyresins are particularly desirable.

A prepreg of the first embodiment is completely covered with resin onone surface, and the resin impregnation ratio must fall within a rangeof 35% to 95%. When molding is conducted without the use of anautoclave, under only vacuum pressure, the inclusion of adeaeratingdeaerating circuit is very important, although thisrequirement has already been well identified in the conventionaltechnology. In this description, the deaeratingdeaerating circuit refersto the portions within the prepreg that have not been impregnated withresin, and these portions act as air pathways. However, if thisdeaeratingdeaerating circuit is too large, then the deaeratingdeaeratingcircuit can remain even after molding, and can cause internal voids andsurface pinholes. As a result of investigating the most appropriate sizefor the deaeratingdeaerating circuit in a prepreg, the inventors of thepresent invention discovered that provided the resin impregnation ratiofalls within a certain preferred range, a satisfactory deaeratingcircuit can be ensured, while satisfactory resin impregnation can stillbe achieved during molding, and they were consequently able to completethe present invention.

This resin impregnation ratio is described below in more detail withreference to the drawings. FIG. 1 is a schematic illustration of aprepreg 10 with a reinforcing fiber substrate in which the fibers arealigned unidirectionally, viewed in a cross section cut perpendicularlyto the direction of the fibers. The matrix resin is supplied fromunderneath in FIG. 1, and the matrix resin 1 impregnates upwards intothe sheet-like reinforcing fiber substrate. In FIG. 1, the portion intowhich the matrix resin 1 has impregnated is shown by the diagonalshading. In FIG. 1, the matrix resin is supplied from underneath, but inthe present invention, the matrix resin can also be supplied from above,and then allowed to impregnate down into the substrate. The crosssection is inspected across at least 80% of the width of the sheet-likereinforcing fiber substrate, and the highest point to which the resinhas penetrated is determined (or in those cases where the resin issupplied from above, the lowest point of penetration is determined). InFIG. 1, the point A represents the highest point for the resin. If theaverage thickness of the sheet-like reinforcing fiber substrate istermed t₁, and the distance from the bottom edge of the sheet-likereinforcing fiber substrate to the point A is termed a, then theimpregnation ratio can be represented by a formula (3) shown below.

Resin impregnation ratio=a/t ₁×100(%)  (3)

The average thickness t₁ of the sheet-like reinforcing fiber substratecan be determined in the manner described below. The length of the linejoining the bottom edge 10 a and the top edge 10 b in a cross sectionthrough the prepreg 10 (this line is deemed the thickness line) is takenas the thickness of the sheet-like substrate. This thickness is measuredat 10 random points, and the average of the thickness values iscalculated and used as the average thickness t₁ of the sheet-likereinforcing fiber substrate. In the case of a sheet-like reinforcingfiber substrate in which the fibers are aligned unidirectionally, theouter contours of the substrate essentially coincide with the thicknessline.

Furthermore, in order to determine the highest point reached by thematrix resin 1, the substrate is best viewed in a cross sectionperpendicular to the direction of the reinforcing fibers, andconsequently in the case of a multiaxial stitched sheet, wherein unlikethe sheet-like reinforcing fiber substrate of the FIG. 1 in which thefibers are aligned unidirectionally, the fibers are layered in alldifferent directions, a cross sectional photograph can be taken througha cross section at any suitable angle.

The cut can be performed with a sharp blade such as a razor blade, andis made with a single cut. The photograph is preferably taken at amagnification of 50 to 100×.

Next is a description of a case in which the sheet-like reinforcingfiber substrate is a woven fabric 20. FIG. 2 shows a method ofdetermining the resin impregnation ratio in those cases where a plainweave fabric is used as the sheet-like reinforcing fiber substrate. Inthe case of a woven fabric, the matrix resin 1 moves along the openportions 21 in the weave, meaning the resin impregnation ratio is bestobserved at a cross-section through those open portions 21. In a similarmanner to that described for the reinforcing fiber substrate in the FIG.1 where the fibers were aligned unidirectionally, the highest point B towhich the matrix resin 1 has penetrated is determined from the crosssection of FIG. 2. If the distance from the bottom edge 20 a of thesheet-like reinforcing fiber substrate to the point B is termed b, thelength of the line joining the bottom edge 20 a and the top edge 20 b ofthe sheet-like reinforcing fiber substrate is deemed the thickness ofthe sheet-like reinforcing fiber substrate, and the average thickness istermed t₂, then the resin impregnation ratio can be determined by aformula (4) shown below. The average thickness t₂ is measured using asimilar method to that described for the case of a reinforcing fibersubstrate in which the fibers are aligned unidirectionally, although inthe case of a woven fabric, the outer contours of the sheet-likereinforcing fiber substrate do not coincide with the thickness line (seeFIG. 2).

Resin impregnation ratio=b/t ₂×100(%)  (4)

The resin impregnation ratio in a prepreg according to the firstembodiment is preferably within a range of 35% to 95%. If the resinimpregnation ratio is less than 35%, then the resin is unable tocompletely fill the non-impregnated portions during molding, meaninginternal voids and surface pinholes remain following molding. If theresin impregnation ratio is at least 40%, then internal voids andsurface pinholes tend not to remain following molding, and ratios of atleast 50% are particularly preferred. In contrast, if the resinimpregnation ratio exceeds 95%, then the formation of a deaeratingcircuit can no longer be ensured, which can also cause residual internalvoids and surface pinholes. If the resin impregnation ratio is no morethan 90%, then it is easier to ensure an adequate deaerating circuit,and resin impregnation ratios of no more than 80% are particularlypreferred.

Furthermore, a prepreg of the present invention must have at least onesurface completely covered with resin. The prepreg is used either bysticking to a molding die, or by generating a multi-ply laminate of theprepreg, and consequently the prepreg requires a suitable level oftackiness. A prepreg of the present invention has at least one surfacecompletely covered with resin, and consequently has a suitable level oftackiness and superior handling properties.

Furthermore, the weight of the sheet-like reinforcing fiber substrate ina prepreg according to the first embodiment is preferably at least 400g/m². A prepreg of the first embodiment contains a deaerating circuit,but during molding the resin penetrates to all corners of the sheet-likereinforcing fiber substrate, enabling the formation of a completelyimpregnated molded product with no internal voids or surface pinholes,and consequently the prepreg is suited to sheet-like reinforcing fibersubstrate with a certain level of thickness. In terms of weight,sheet-like reinforcing fiber substrates with a weight of at least 400g/m² are preferred. Weights of at least 600 g/m² are even moredesirable, and weights of at least 700 g/m² are particularly preferred.

Furthermore, the thickness of the sheet-like reinforcing fiber substratein a prepreg of the first embodiment is preferably at least 200 μm. Aprepreg of the first embodiment can yield a favorable molded productwith no internal voids at atmospheric pressure, even if the fluidity ofthe matrix resin is poor. Accordingly, a favorable molded product can beachieved even if the sheet-like reinforcing fiber substrate isconsiderably thick, and in actual fact, the effects of the presentinvention are manifested most markedly with thicker substrates. Theeffects are particularly marked for thick materials where the thicknessof the sheet-like reinforcing fiber substrate is at least 300 μm. Thethickness is determined by dividing the mass per unit of surface area ofthe sheet-like reinforcing fiber substrate by the density of thereinforcing fibers.

In those cases where the matrix resin of a prepreg of the firstembodiment is a thermosetting resin composition, the thermosetting resincomposition preferably comprises a thermoplastic resin that is notdissolved within the thermosetting resin composition. This thermoplasticresin is preferably in the form of short fibers, and the length of thoseshort fibers is preferably within a range of 1 to 50 mm. Furthermore,the size of the fibers is preferably no more than 300 tex.

When prepregs of this first embodiment are laminated and molded, thenduring the molding process, the short fibers of thermoplastic resinwithin the thermosetting resin composition are filtered by thereinforcing fibers that make up the sheet-like reinforcing fibersubstrate, and end up positioned at the surface of each of the laminatedsheet-like reinforcing fiber substrates, namely, positioned between thelayers of the laminate. This improves the interlayer peeling resistancemarkedly, providing a superior interlayer reinforcement effect.

In order to ensure an efficient manifestation of this interlayerreinforcement effect, the thermoplastic resin preferably exist asfibers. If other shapes such as fine particles are used instead of theaforementioned short fibers, then the thermoplastic resin is notefficiently filtered by the sheet-like reinforcing fiber substrateduring the molding process, and migrates into the interior of thesheet-like reinforcing fiber substrate together with the thermosettingresin during the impregnation process, meaning efficient interlayerreinforcement can not be achieved.

Accordingly, the thermoplastic resin is preferably in the form of shortfibers. In addition, the length of these fibers is preferably within arange of 1 to 50 mm. If the length of the short fibers is less than 1mm, then the fibers penetrate into the interior of the sheet-likereinforcing fiber substrate, in a similar manner to fine particles,making it difficult to achieve an efficient improvement in theinterlayer peeling resistance. Considering the fact that a certain sizeis necessary, fibers with a length of at least 3 mm are particularlypreferred. In contrast, if the length of the fibers exceeds 50 mm, thenthe fibers become overly long, preparation of the thermosetting resincomposition becomes extremely problematic, and dispersing the fibersuniformly through the thermosetting resin composition also becomesdifficult, which causes an undesirable deterioration in the uniformityof the interlayer reinforcement. Fiber lengths of no more than 30 mm areparticularly preferred.

Furthermore in those cases where the thermoplastic resin exists as shortfibers, the size of those fibers is preferably no more than 300 tex. Theshort fibers of the thermoplastic resin may exist either as filamentsformed from single strands of fiber, or as multifilaments comprising aplurality of individual fiber strands. If the size of the fibers exceed300 tex, then the thickness of the layer formed by the accumulated shortfibers between the substrate layers becomes overly thick, and there is adanger of the short fibers interfering with the reinforcing fibers ofthe sheet-like reinforcing fiber substrates, causing bending of thereinforcing fibers, and an undesirable deterioration in the mechanicalstrength of the molded composite material. Fiber sizes of no more than100 tex are even more desirable, and sizes of no more than 50 tex areparticularly preferred. There are no particular restrictions at the fineend of the size scale, and satisfactory effects can be achieved forsizes of at least 1 tex.

Examples of suitable thermoplastic resins include polyaramid, polyester,polyacetal, polycarbonate, polyphenylene oxide, polyphenylene sulfide,polyallylate, polyimide, polyetherimide, polysulfone, polyamide,polyamide-imide, and polyetheretherketone. Furthermore, elastomers canalso be used favorably instead of the thermoplastic resin. Examples ofsuitable elastomers include synthetic rubbers such as butyl rubber,isoprene rubber, nitrile rubber, and silicon rubber, as well as naturalrubbers such as latex.

The quantity of the thermoplastic resin within the thermosetting resincomposition is preferably within a range of 1 to 100 parts by mass per100 parts by mass of the thermosetting resin composition. If thequantity of the thermoplastic resin is less than 1 part by mass, thenthe effect of the invention in improving the FRP interlayer peelingresistance weakens undesirably. Quantities of the thermoplastic resin ofat least 5 parts by mass are even more desirable, and quantities of atleast 10 parts by mass are particularly preferred. In contrast, if thequantity exceeds 100 parts by mass, then the proportion of thethermoplastic resin becomes overly high, which can cause a deteriorationin the impregnation of the matrix resin into the sheet-like reinforcingfiber substrate, and the quantity of the matrix resin relative to thesheet-like reinforcing fiber substrate can become too high, causing anundesirable deterioration in the FRP mechanical strength.

Although there are no particular restrictions on the process forproducing a prepreg according to the first embodiment, a productionprocess in which a resin is supplied, using a hot melt method, to onesurface of a sheet-like reinforcing fiber substrate comprisingreinforcing fibers, and the structure is then heating and pressed,causing the resin to migrate through to a position close to the oppositesurface of the substrate is preferred. In such a process, the heatingtemperature and the pressure applied during the pressing step areadjusted to control the degree of migration of the resin and the mannerof the migration, thus adjusting the resin impregnation ratio to a valuewithin a range of 35% to 95%. The hot melt method is a prepregproduction process in which no solvent is used, and the viscosity of theresin is lowered by raising the temperature of the resin, therebycausing the resin to impregnate the substrate, and amongst the possibleforms of the hot melt method that can be used for producing a prepreg, adouble film process, in which the resin is supplied from both the upperand lower surfaces of the sheet-like reinforcing fiber substrate isusually preferred in terms of the impregnation results. However, in thefirst embodiment, because one surface of the prepreg must be availablefor forming the deaerating circuit and can therefore not be impregnatedwith resin, the double film process is not suitable as the process forproducing a prepreg according to the first embodiment. As describedabove, a single film process in which the resin is supplied from onesurface of the sheet-like reinforcing fiber substrate is preferred.

The matrix resin in a prepreg of the first embodiment is a thermosettingresin composition, and in those cases where the composition alsocomprises a thermoplastic resin that has not been dissolved in thethermosetting resin composition, the thermoplastic resin is preferablyblended into the composition during the mixing and preparation of thethermosetting resin composition, and the resulting composition is thenconverted to a film form, and impregnated into the sheet-likereinforcing fiber substrate.

A second embodiment of the present invention is a prepreg comprising asheet-like reinforcing fiber substrate and a matrix resin, wherein thematrix resin exists on both surfaces of the sheet-like reinforcing fibersubstrate, and the portion inside the sheet-like reinforcing fibersubstrate into which the matrix resin has not been impregnated iscontinuous.

There are no particular restrictions on the reinforcing fibers used inthe sheet-like reinforcing fiber substrate used in a prepreg of thissecond embodiment, and examples of suitable fibers include carbon fiber,graphite fiber, aramid fiber, silicon carbide fiber, alumina fiber,boron fiber, high-strength polyethylene fiber, PBO fiber, and glassfiber, and these fibers can be used either singularly, or in mixtures oftwo or more different types of fiber. Of these reinforcing fibers,either carbon fiber which offers superior specific strength andinelasticity, or glass fiber which offers more favorable costperformance, is preferred.

Furthermore, there are also no particular restrictions on the form ofthe sheet-like reinforcing fiber substrate used in the prepreg of thissecond embodiment, and suitable examples include unidirectionalmaterials in which the reinforcing fibers are aligned unidirectionally,woven fabrics, knit fabrics, braided fabrics, stitched sheets whereinmultiple fabrics are laminated, either unidirectionally or in variousdirections, and then stitched, as well as mats and non-woven fabricscomprising short fibers. Of these, woven fabrics, stitched sheets, matsand non-woven fabrics offer superior levels of stability for thesheet-like reinforcing fiber substrate, and because an intermediatematerial for FRP molding of the present invention offers superiorhandling properties, it is preferred as the sheet-like reinforcing fibersubstrate.

In a prepreg according to the second embodiment, the portion inside thesheet-like reinforcing fiber substrate into which the matrix resin hasnot been impregnated must be a continuous portion. In the secondembodiment, this non-impregnated portion functions as the deaeratingcircuit, and the existence of this deaerating circuit means that themolded FRP can be formed without internal voids and surface pinholes.However, if this deaerating circuit is segmented by the matrix resin,then the air that is enclosed by the matrix resin becomes extremelydifficult to remove, and can give rise to internal voids and surfacepinholes.

The following method can be used for determining whether or not theportion inside the sheet-like reinforcing fiber substrate into which thematrix resin has not been impregnated is continuous. First, the prepregis cut at a right angle to the lengthwise direction of the prepreg. Thecut is performed in a single action, using an NT cutter or the like. Ifa number of cutting strokes are used, then the surface of the cutbecomes undesirably messy. The two edges of the cut surface in the widthdirection are trimmed off, with 10% of the width dimension removed fromeach edge. The entirety of the remaining 80% portion across the widthdirection is then inspected to confirm that the portion into which thematrix resin has not been impregnated is continuous. The inspection ispreferably conducted using a magnifying glass or the like.

FIG. 3 shows a prepreg 30 formed from a sheet-like reinforcing fibersubstrate comprising matrix resin-impregnated layers 31 that have beenimpregnated with a matrix resin 1, and a matrix resin non-impregnatedlayer 32. This figure represents an example where, when the matrix resin1 is impregnated, the matrix resin non-impregnated layer 32 is formed asa continuous layer.

In contrast, FIG. 5 shows a prepreg 50 formed from a sheet-likereinforcing fiber substrate comprising matrix resin-impregnated layers51 that have been impregnated with a matrix resin 1, and a matrix resinnon-impregnated layer 52. This figure represents an example where, whenthe matrix resin 1 is impregnated, the matrix resin non-impregnatedlayer 52 is formed in a non-continuous manner.

There are no particular restrictions on the matrix resin used in aprepreg of the second embodiment, and both thermosetting resins andthermoplastic resins can be used, although from the viewpoints of thehandling of the prepreg, such as the tack and drape characteristics, andthe moldability, thermosetting resins are preferred. Examples ofsuitable thermosetting resins include epoxy resins, phenol resins, vinylester resins, unsaturated polyester resins, bismaleimide resins, BTresins, cyanate ester resins, and benzoxazine resins. In terms ofhandling properties and the properties of the resulting cured product,epoxy resins, bismaleimide resins, BT resins, and cyanate ester resinsare preferred, and of these, epoxy resins are particularly desirable.

Furthermore, the weight of the sheet-like reinforcing fiber substrate ina prepreg according to the second embodiment is preferably at least 400g/m². A prepreg of the second embodiment contains a deaerating circuit,but during molding the resin penetrates to all corners of the sheet-likereinforcing fiber substrate, enabling the formation of a completelyimpregnated molded product with no internal voids or surface pinholes.Consequently the prepreg is suited to sheet-like reinforcing fibersubstrate with a certain level of thickness. In terms of weight,sheet-like reinforcing fiber substrates with a weight of at least 200g/m² are preferred. Weights of at least 600 g/m² are even moredesirable, and weights of at least 700 g/m² are particularly preferred.

Furthermore, the thickness of the sheet-like reinforcing fiber substratein a prepreg of the second embodiment is preferably at least 200 μm. Aprepreg of the second embodiment can yield a favorable molded productwith no internal voids at atmospheric pressure, even if the fluidity ofthe matrix resin is poor. Accordingly, a favorable molded product can beachieved even if the sheet-like reinforcing fiber substrate isconsiderably thick, and in actual fact, the effects of the presentinvention are manifested most markedly with thicker substrates. Theeffects are particularly marked for thick materials where the thicknessof the sheet-like reinforcing fiber substrate is at least 300 μm. Thethickness is determined by dividing the mass per unit of surface area ofthe sheet-like reinforcing fiber substrate by the density of thereinforcing fibers.

In those cases where the matrix resin of a prepreg of the secondembodiment is a thermosetting resin composition, the thermosetting resincomposition preferably comprises a thermoplastic resin that is notdissolved within the thermosetting resin composition. This thermoplasticresin is preferably in the form of short fibers, and the length of thoseshort fibers is preferably within a range of 1 to 50 mm. Furthermore,the size of the fibers is preferably no more than 300 tex.

When prepregs of this second embodiment are layered and molded, thenduring the molding process, the short fibers of thermoplastic resinwithin the thermosetting resin composition are filtered by thereinforcing fibers that make up the sheet-like reinforcing fibersubstrate, and end up positioned at the surface of each of the laminatedsheet-like reinforcing fiber substrates, namely, positioned between thelayers of the laminate. This improves the interlayer peeling resistancemarkedly, providing a superior interlayer reinforcement effect.

In order to ensure an efficient manifestation of this interlayerreinforcement effect, the thermoplastic resin preferably exist asfibers. If other shapes such as fine particles are used instead of thesethermoplastic resin short fibers, then the thermoplastic resin is notefficiently filtered by the sheet-like reinforcing fiber substrateduring the molding process, and migrates into the interior of thesheet-like reinforcing fiber substrate together with the thermosettingresin during the impregnation process, meaning efficient interlayerreinforcement can not be achieved.

Accordingly, the thermoplastic resin is preferably in the form of shortfibers. In addition, the length of these fibers is preferably within arange of 1 to 50 mm. If the length of the short fibers is less than 1mm, then the fibers penetrate into the interior of the sheet-likereinforcing fiber substrate, in a similar manner to fine particles,making it difficult to achieve an efficient improvement in theinterlayer peeling resistance. Considering the fact that a certain sizeis necessary, fibers with a length of at least 3 mm are particularlypreferred. In contrast, if the length of the fibers exceeds 50 mm, thenthe fibers become overly long, preparation of the thermosetting resincomposition becomes extremely problematic, and dispersing the fibersuniformly through the thermosetting resin composition also becomesdifficult, which causes an undesirable deterioration in the uniformityof the interlayer reinforcement. Fiber lengths of no more than 30 mm areparticularly preferred.

Furthermore, in those cases where the thermoplastic resin exists asshort fibers, the size of those fibers is preferably no more than 300tex. The short fibers of the thermoplastic resin may exist either asfilaments formed from single strands of fiber, or as multifilamentscomprising a plurality of individual fiber strands. If the size of thefibers exceed 300 tex, then the thickness of the layer formed by theaccumulated short fibers between the substrate layers becomes overlythick, and there is a danger of the short fibers interfering with thereinforcing fibers of the sheet-like reinforcing fiber substrates,causing bending of the reinforcing fibers, and an undesirabledeterioration in the mechanical strength of the molded compositematerial. Single fiber sizes of no more than 100 tex are even moredesirable, and sizes of no more than 50 tex are particularly preferred.There are no particular restrictions at the fine end of the single fibersize scale, and satisfactory effects can be achieved for sizes of atleast 1 tex.

Examples of suitable thermoplastic resins include polyaramid, polyester,polyacetal, polycarbonate, polyphenylene oxide, polyphenylene sulfide,polyallylate, polyimide, polyetherimide, polysulfone, polyamide,polyamide-imide, and polyetheretherketone. Furthermore, elastomers canalso be used favorably instead of the thermoplastic resin. Examples ofsuitable elastomers include synthetic rubbers such as butyl rubber,isoprene rubber, nitrile rubber, and silicon rubber, as well as naturalrubbers such as latex.

The quantity of the thermoplastic resin within the thermosetting resincomposition is preferably within a range of 1 to 100 parts by mass per100 parts by mass of the thermosetting resin composition. If thequantity of the thermoplastic resin is less than 1 part by mass, thenthe effect of the invention in improving the FRP interlayer peelresistance weakens undesirably. Quantities of at least 5 parts by massare even more desirable, and quantities of at least 10 parts by mass areparticularly preferred. In contrast, if the quantity exceeds 100 partsby mass, then the proportion of the thermoplastic resin becomes overlyhigh, which can cause a deterioration in the impregnation of the matrixresin into the sheet-like reinforcing fiber substrate, and the quantityof the matrix resin relative to the sheet-like reinforcing fibersubstrate can become too high, causing an undesirable deterioration inthe FRP mechanical strength.

In those cases where the matrix resin used in a prepreg of the secondembodiment is a thermosetting resin composition, the thermosetting resincomposition is preferably able to be cured at 90° C. for 2 hours, andeven more preferably at 80° C. for 2 hours. A prepreg of the secondembodiment can yield a favorable molded product with no internal voidsat atmospheric pressure, even if the fluidity of the thermosetting resincomposition that functions as the matrix resin is poor, andconsequently, the invention is suited to comparatively low temperaturecuring of the thermosetting resin composition.

On the other hand, prepregs must typically display favorable handlingcharacteristics at room temperature. Two major factors in determiningthe handling characteristics are the tack (the degree of stickiness) andthe drape characteristics (the flexibility), and in order to optimizethe tack and drape characteristics, the thermosetting resin compositionthat functions as the matrix resin must have a viscosity that fallswithin a certain range. If the viscosity of the thermosetting resincomposition is too low, then the tackiness is too powerful, makinghandling extremely difficult, whereas if the viscosity is too high, thenthe tackiness is overly weak, and the drape characteristics caneffectively disappear, which also makes handling very difficult. Hence,in order to ensure favorable handling characteristics for the prepreg,the thermosetting resin composition must have a viscosity that fallswithin an appropriate range. Accordingly, if a thermosetting resincomposition cures at lower temperatures, then this means that thecomposition is capable of curing while still at a relatively higherviscosity, and is consequently suitable as a thermosetting resincomposition for a prepreg of the second embodiment, which is capable ofyielding a favorable molded product even with comparatively poorfluidity.

A determination as to whether or not the thermosetting resin compositioncan be cured in 2 hours at 90° C. can be performed in the followingmanner. Namely, either the thermosetting resin composition by itself, ora sheet-like reinforcing fiber substrate that has been impregnated withthe thermosetting resin composition is molded for 2 hours at 90° C. inan oven. If the external appearance suggests that the resulting curedproduct has definitely cured, then the composition is deemed to becurable in 2 hours at 90° C. A determination as to whether or not athermosetting resin composition can be cured in 2 hours at 80° C. can beconducted in a similar manner. In those cases where determining whetheror not the composition has cured is difficult, the Tg value of themolded product is measured, and the composition is deemed to have curedif the Tg value is at least 30° C.

Typically, when an intermediate material for FRP molding such as aprepreg is produced, the process for impregnating the matrix resin intothe sheet-like reinforcing fiber substrate involves applying a thincoating of a thermosetting resin composition on the surface of a releasesheet or a polyolefin film or the like, and then supplying thethermosetting resin composition on the surface of a reinforcing fibersubstrate to achieve impregnation. These impregnation processes can bebroadly classified into single film processes in which the resincomposition is supplied and impregnated from only one surface of thereinforcing fiber substrate, and double film processes in which theresin composition is supplied and impregnated from both surfaces of thereinforcing fiber substrate. In the second embodiment, supply of theresin composition using a double film process is extremely desirable.The reason for this preference is that the second embodiment assumes theuse of thermosetting resin compositions that are capable of curing atlow temperatures, namely, thermosetting resin compositions withcomparatively low fluidity. FIG. 3 and FIG. 4 are schematicillustrations showing the prepregs obtained when the same quantity ofresin is supplied to sheet-like reinforcing fiber substrates ofidentical thickness, using a double film process and a single filmprocess respectively.

FIG. 3 shows a prepreg 30 comprising matrix resin-impregnated layers 31and a matrix resin non-impregnated layer 32, formed by impregnating amatrix resin 1 from both surfaces of a sheet-like reinforcing fibersubstrate.

FIG. 4 shows a prepreg 40 comprising a matrix resin-impregnated layer 41and a matrix resin non-impregnated layer 42, formed by impregnating amatrix resin 1 from one surface of a sheet-like reinforcing fibersubstrate.

As is evident from FIG. 3 and FIG. 4, if prepregs of the secondembodiment are produced by either a single film process or a doable filmprocess, then the prepreg produced by the double film process tends tohave a wider non-impregnated layer 42 than the prepreg produced by thesingle film process. As a result, using a double film process ispreferred, as it enables a reduction in the quantity of thermosettingresin composition that must migrate in order to fill the deaeratingcircuit during the molding step, thus ensuring that the deaeratingcircuit is completely filled prior to the completion of curing.

When the matrix resin is supplied to the sheet-like reinforcing fibersubstrate, it is preferably stuck to the substrate at room temperature,without heating. However, in those cases where the viscosity of thematrix resin at room temperature is very high, the resin may be heatedslightly to improve the level of fluidity. However even in such cases,in order to ensure that a continuous resin non-impregnated portion suchas that described below is left inside the substrate, any heating ispreferably conducted at no more than 40° C., and even more preferably atno more than 30° C.

In those cases where the matrix resin for a prepreg according to thesecond embodiment is a thermosetting resin composition, and thatcomposition comprises a thermoplastic resin that is not dissolved withinthe thermosetting resin composition, the thermoplastic resin ispreferably blended into the composition during the mixing andpreparation of the thermosetting resin composition, and the resultingcomposition is then converted to a film form, and impregnated into thesheet-like reinforcing fiber substrate.

A prepreg according to a third embodiment of the present inventioncomprises a matrix resin impregnated into a reinforcing fiber wovenfabric, wherein at least one surface displays a sea-and-island-typepattern comprising resin-impregnated portions (island portions) wherethe matrix resin is present at the surface and fiber portions (seaportions) where the matrix resin is not present at the surface, thesurface coverage ratio of the matrix resin on surfaces with thesea-and-island-type pattern is within a range of 3% to 80%, and theweave intersection coverage ratio for the island portions, asrepresented by a formula (5) shown below, is at least 40%.

Island portions weave intersection coverage ratio (%)=(T/Y)×100  (5)

(wherein, T represents the number of island portions that cover weaveintersections, and Y represents the total number of weave intersectionsof the reinforcing fiber fabric on the surface with thesea-and-island-type pattern).

A prepreg of the third embodiment is formed by impregnating areinforcing fiber woven fabric with a matrix resin. Suitable examples ofthe reinforcing fibers used in forming the woven fabric include carbonfiber, glass fiber, aramid fiber, boron fiber, metal fiber, PBO fiber,and high-strength polyethylene fiber, although of these, carbon fiber isparticularly preferred as it results in more favorable mechanicalproperties following molding, and is also very lightweight. Furthermore,suitable examples of the form of the woven fabric include plain weavefabric, twill fabric, satin weave fabric, stitched sheets in which longfibers that have been aligned unidirectionally are stitched together,and blind weave. Woven fabrics in which the warp and the woof usedifferent fibers can also be used.

Furthermore, a reinforcing fiber woven fabric used in the thirdembodiment preferably displays a fiber weight of no more then 1500 g/m².If the fiber weight exceeds 1500 g/m², then the density of thereinforcing fibers becomes overly high, and achieving a fabric withsuperior mechanical properties becomes difficult. Fiber weights of nomore than 1000 g/m² are even more desirable. There are no particularrestrictions on the lower limit for the fiber weight. However, theweight is preferably at least 50 g/m², and even more preferably 75 g/m²or greater. If the fiber weight is less than 50 g/m², then in thosecases where a large FRP is required, the number of layers of prepregmust be increased significantly, which can lead to cost increases.

There are no particular restrictions on the matrix resins that can beused in a prepreg according to the third embodiment, and suitable resinsinclude thermosetting resins such as epoxy resins, polyester resins,vinyl ester resins, phenol resins, maleimide resins, polyimide resins,and BT resins comprising a combination of a cyanate and a bismaleimideresin, as well as thermoplastic resins such as acrylic resins andpolyetheretherketones. Matrix resins that improve the strength of theproduct FRP are preferred, and of the above resins, epoxy resins areparticularly preferred, as their superior adhesion to reinforcing fibersimproves the mechanical properties of the product FRP.

Specific examples of suitable epoxy resins include bifunctional resinssuch as bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol Sepoxy resins, biphenyl epoxy resins, naphthalene epoxy resins,dicyclopentadiene epoxy resins, fluorene epoxy resins, and modifiedresins thereof; and trifunctional or greater polyfunctional epoxy resinssuch as phenol novolac epoxy resins, cresol epoxy resins, glycidylamineepoxy resins such as tetraglycidyldiaminodiphenylmethane,triglycidylaminophenol and tetraglycidylamine, glycidyl ether epoxyresins such as tetrakis(glycidyloxyphenyl)ethane andtris(glycidyloxymethane), as well as modified resins thereof; andcombinations of one or more of the above resins can also be used as thematrix resin.

The above epoxy resin compositions may also contain curing agents suchas diphenylmethane, diaminodiphenylsulfone, aliphatic amines, imidazolederivatives, dicyandiamide, tetramethylguanidine, thiourea adducts ofamines, carboxylic acid hydrazides, carboxylic acid amides, polyphenolcompounds, polymercaptans, and boron trifluoride ethyl amine complex, ormaterials obtained by preliminary reaction between an epoxy resin and aportion of one of the above curing agents. In addition, by also blendingin a curing catalyst such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea orphenyldimethylurea, the curing time can be shortened, thereby shorteningthe molding time.

In addition, in those cases where the matrix resin in the thirdembodiment is a thermosetting resin composition, the minimum viscosityfor the thermosetting resin composition is preferably no more than 1000poise. If a high-viscosity thermosetting resin composition with aminimum viscosity exceeding 1000 poise is used, then the fluidity of thethermosetting resin composition deteriorates. In a prepreg of the thirdembodiment, the thermosetting resin composition fills the deaeratingcircuit, which has been complete the role, during molding, but if thefluidity of the thermosetting resin composition is poor, then themolding process may finish before this filling step is complete, meaningthere is a danger that any portions of residual deaerating circuit willform internal voids. In order to prevent this occurring, the weight ofthe resin must be increased, resulting in an undesirable increase incost. Accordingly, lower minimum viscosity values are preferred, andvalues of no more than 500 poise are particularly desirable.

In the third embodiment, the minimum viscosity refers to the lowestviscosity value observed when the temperature of the thermosetting resinis raised from room temperature at a rate of 5° C./minute. The minimumviscosity of the thermosetting resin composition can be determined bymeasuring the dynamic viscoelasticity of the composition, while thetemperature is raised from room temperature at a rate of 5° C./minute.

In a prepreg of the third embodiment, at least one surface displays asea-and-island-type pattern comprising resin-impregnated portions(island portions) where the resin composition is present at the surfaceand fiber portions (sea portions) where the resin composition is notpresent at the surface, and the surface coverage ratio of the resin onsurfaces with the sea-and-island-type pattern is within a range of 3% to80%.

First is a description of the sea-and-island-type pattern, withreference to the drawings. FIG. 6 is a schematic illustration showingthe surface of a prepreg according to a third embodiment of the presentinvention, wherein a resin composition has been impregnated into onesurface of a plain weave reinforcing fiber woven fabric to form asea-and-island-type pattern. The surface of the woven fabric 60 producedfrom woven reinforcing fibers comprises island portions 61 and seaportions 62. Of the island portions 61, those that exist in isolation ata single weave intersection 64 are labeled as island portions 61 a, andthose that are linked with adjacent island portions are labeled asisland portions 61 b. By forming the island portions 61 in this type ofscattered arrangement across the surface, the sea portions 62 act as thedeaerating circuit during molding of the prepreg. The spacing betweenadjacent weave intersections 64 is labeled as the distance 63.

In a prepreg of the third embodiment, the surface coverage ratio of theresin on those surfaces with the sea-and-island-type pattern must fallwithin a range of 3% to 80%. Here, the surface coverage ratio refers tothe ratio of the area of the island portions 61 relative to the surfacearea of the entire surface with the sea-and-island-type pattern.

If this surface coverage ratio is less than 3%, then the tackiness ofthe sea-and-island-type patterned surface of the prepreg is overly poor,causing a deterioration in the prepreg handling properties. In contrast,if the surface coverage ratio exceeds 80%, then the deaerating circuitfor the prepreg is almost completely blocked off, which can causeinternal voids and surface pinholes. In terms of achieving a favorablebalance between tackiness and the size of the deaerating circuit,surface coverage ratios of 5% or more is preferred, and 60% or less isparticularly preferred.

Furthermore, in a prepreg of the third embodiment, the weaveintersection coverage ratio for the island portions 61 on thesea-and-island-type patterned surface, as represented by a formula (6)below, is at least 40) %.

Island portions weave intersection coverage ratio (%)=(T/Y)×100  (6)

T represents the number of island portions that cover weaveintersections, and Y represents the total number of weave intersectionsof the reinforcing fiber woven fabric on the surface with thesea-and-island-type pattern. In the third embodiment, a weaveintersection 64 refers to an intersection between the warp and the woof.

For example, in FIG. 6, the number of island portions 61 covering weaveintersections 64 of the reinforcing fiber fabric is 11, namely T=11. Onthe other hand, in this figure Y=15, meaning that in the example shown,the island portions weave intersection coverage ratio is(11/15)×100=73%.

In contrast, FIG. 7 represents a case where the surface of the wovenfabric 60 contains a larger proportion of linked island portions 61 b.In FIG. 7, the island portions weave intersection coverage ratio ofisland portions 61 is calculated from T=3 and Y=15, and yields a valueof (3/15)×100=20%.

When calculating the number T of island portions that cover weaveintersections in the present invention, resin-impregnated portions 65that do not cover a weave intersection of the reinforcing fiber fabricare not counted.

When the resin surface coverage ratio is within the range from 3% to80%, if the weave intersection coverage ratio for the island portions 61is less than 40%, then as shown in FIG. 7, the probability of theexistence of a sea portion 62 that is totally enclosed by an islandportion 61 on the sea-and-island-type patterned surface increases. Insuch a case, the air that reaches the fabric surface through thedeaerating circuit during molding has no where to escape, increasing thelikelihood of undesirable pinhole formation.

In those cases where both surfaces of the fabric are sea-and-island-typepatterned surfaces, the surface coverage ratio must be within a range of3% to 80% on both surfaces, and the weave intersection coverage ratiofor the island portions 61 is preferably at least 40% on both surfaces.

In terms of productivity and the like, the most preferred process forproducing a prepreg according to the third embodiment is a process inwhich a resin composition is applied to a resin support sheet, thismatrix resin supported on the resin support sheet is bonded to onesurface of a reinforcing fiber woven fabric, a protective film isaffixed to the other surface of the reinforcing fiber woven fabric toprevent the adhesion of any foreign matter, and heating and/or pressureis then used to impregnate the matrix resin into the reinforcing fiberwoven fabric, thus forming a prepreg wherein the surface of thereinforcing fiber woven fabric on the side of the protective filmdisplays a sea-and-island-type pattern comprising resin-impregnatedportions (island portions) where the matrix resin is present at thesurface, and fiber portions (sea portions) where the resin compositionis not present at the surface.

The heating conditions used within this process preferably employ atemperature that ensures that the viscosity of the matrix resin reachesno more than 5000 poise, whereas the pressure conditions preferably usea linear pressure of 49 to 780 kPa, thus ensuring a prepreg with asatisfactory deaerating circuit. In the case of an epoxy resincomposition, the temperature required to ensure a viscosity of no morethan 5000 poise is typically within a range of 40 to 80° C.

The protective film used in the process for producing a prepregaccording to the third embodiment preferably displays favorablereleasability relative to the matrix resin, and suitable examplesinclude release sheets or polyethylene film that have beensurface-treated with silicone.

Furthermore, the resin support sheet can also use a resin film formedfrom a polyolefin and a release sheet or the like. In addition, when thematrix resin is applied to the resin support sheet, a process can beused which employs a resin support sheet with an irregular surface, sothat when the matrix resin is applied to this resin support sheet, andthe matrix resin-coated surface of the resin support sheet and thereinforcing fiber woven fabric are stuck together, only the matrix resinapplied to the convex portions of the resin support sheet is transferredto, and impregnated into the reinforcing fiber woven fabric, thusgenerating a sea-and-island-type pattern.

If a prepreg of the third embodiment is produced using this process,then the matrix resin is impregnated into the reinforcing fiber wovenfabric mainly at the weave intersections points, and is exuded out atthe weave intersections on the opposite surface (the protective filmside) of the fabric, impregnating the reinforcing fibers in the vicinityof the surface. As a result, this process results in almost no islandportions that do not cover weave intersections.

Furthermore, in a different process from that described above, thematrix resin can be applied directly to the surface of the reinforcingfiber woven fabric that is to become the sea-and-island-type patternedsurface, either uniformly or in a non-uniform manner, or by sticking aresin support sheet to the surface, and in a similar manner to thatdescribed above, this process also causes the matrix resin to impregnateinto the fabric along the weave intersections, so that followingimpregnation, almost all of the matrix resin is connected to an islandportion that covers a weave intersection.

However, although production is possible using this alternative process,adjusting the impregnation conditions (the temperature and pressureconditions) to ensure a favorable surface coverage ratio and a favorableisland portions weave intersection coverage ratio requires considerableskill.

In other words, regardless of the process used to produce a prepregaccording to the third embodiment, during impregnation the matrix resinpenetrates into the interior of the woven fabric along the weaveintersections from the surface, and exudes from the weave intersectionson the opposite surface, meaning the number of island portions that donot cover weave intersections is essentially nil.

A fourth embodiment of the present invention is an intermediate materialfor FRP molding in which a substrate containing essentially noimpregnated thermosetting resin composition is bonded to at least oneside of a prepreg comprising a matrix resin and reinforcing fibers,wherein the ratio (B)/(A) between the thickness (A) of the prepreg, andthe thickness (B) of the substrate is within a range of 0.1 to 2.5.

(Matrix Resin)

There are no particular restrictions on the matrix resin used in thefourth embodiment, although from the viewpoints of the handling of theprepreg, such as the tack and drape characteristics, and themoldability, thermosetting resin compositions are preferred. Examples ofthe thermosetting resin that forms the main component of thethermosetting resin composition include epoxy resins, phenol resins,bismaleimide resins, BT resins, cyanate ester resins, and benzoxazineresins, although epoxy resins are preferred, as their superior adhesionto reinforcing fibers improves the mechanical properties of the productFRP. Furthermore, phenol resins are also preferred, as not only do theydisplay excellent flame retardancy, but they are also ideally suited tolacquer-type prepreg production processes.

(Reinforcing Fibers)

There are no particular restrictions on the reinforcing fibers used inthe prepreg of this fourth embodiment, and any reinforcing fibers thatoffer high strength and high elasticity can be used, including glassfiber, carbon fiber, aramid fiber, boron fiber, and PBO fiber. Of these,reinforcing fibers that use either glass fiber or carbon fiber arepreferred, as they offer excellent balance between elasticity andstrength, and yield FRPs with excellent mechanical properties.

(Production Process for Prepreg)

The process for producing a prepreg used in the fourth embodiment mayutilize the hot melt process described above, although even when aprepreg that has been produced by a lacquer process is used, ovenmolding is still capable of producing a molded product with no internalvoids or surface pinholes, meaning the effects of the present inventionare particularly significant for prepregs produced by a lacquer process.

A lacquer process is a prepreg production process in which thereinforcing fibers are impregnated with a thermosetting resincomposition that has been diluted with a solvent, and the solvent issubsequently removed. Suitable methods for impregnating the reinforcingfibers with the solvent solution include immersing the reinforcingfibers in the thermosetting resin composition solution, or applying thesolution to a roller and then transferring the solution to thereinforcing fibers using the roller. However, effecting the impregnationby immersing the reinforcing fibers in the solution provides superiorimpregnation of the thermosetting resin composition solution into thereinforcing fibers, and is consequently preferred. Furthermore, suitablemethods for removing the solvent include warm or hot air dryers, ordrying under reduced pressure, although warm air drying is the mostpreferred in terms of productivity.

(Prepreg and Substrate)

An intermediate material for FRP molding according to the presentinvention comprises an aforementioned prepreg with a substratecontaining essentially no impregnated thermosetting resin compositionbonded to at least one side of the prepreg. By allowing this substrateto function as a deaerating circuit, any internal air pockets can beremoved easily during molding, meaning the substrate performs animportant role in preventing the occurrence of internal voids andsurface pinholes within the molded product. If a substrate is bonded toboth surfaces of a prepreg, then the deaerating circuit is larger thanthat generated when a substrate is bonded to only one surface, which canoffer advantages in some cases. However, the loss of tackiness on bothsurfaces can cause a deterioration in productivity, and as such, in mostcases, a substrate is preferably only bonded to one surface, and theother surface is left with the prepreg exposed, thus retaining favorabletackiness.

As described above, in an intermediate material for FRP moldingaccording to the fourth embodiment, the substrate acts as a deaeratingcircuit during molding, acting as a pathway for guiding air out of thestructure during the molding process. However, during molding, thesubstrate must also become impregnated with the matrix resin that isimpregnated within the reinforcing fibers, so that following molding, asingle integrated body molded product is obtained that contains nointernal voids or surface pinholes. As a result, the substrate mustcomprise sufficient air gaps to function satisfactorily as thedeaerating circuit, but must also have a quantity of air gaps that canbe completely filled by the matrix resin during the molding process.Accordingly, the quantity of air gaps within the substrate must bematched with the prepreg used in the fourth embodiment of the presentinvention. As a result of careful investigations, it was discovered thata favorable quantity of air gaps could be achieved by controlling theratio between the respective thickness values for the prepreg and thesubstrate. Specifically, the ratio (B)/(A) between the thickness (A) ofthe prepreg, and the thickness (B) of the substrate must be within arange of 0.1 to 2.5. As described above, the substrate must comprisesufficient air gaps to function satisfactorily as the deaeratingcircuit, but those air gaps must be completely filled by the matrixresin during the molding process. The lower limit of the above range iseven more preferably 0.15 or greater, and most preferably 0.2 orgreater. If the ratio is less than 0.1, then ensuring sufficient airgaps for the substrate to function satisfactorily as the deaeratingcircuit becomes difficult, and air can remain trapped following molding.On the other hand, the upper limit of the above range is even morepreferably no more than 1.5, and is most preferably 1.1 or less. If theratio exceeds 2.5, then the air gaps may not be completely filled duringthe molding process, meaning residual air may be left following molding.

(Measurement of the Thickness of the Prepreg and the Substrate)

In this description, the thickness (A) of the prepreg and the thickness(B) of the substrate refer to values measured using vernier calipers.During measurement, care must be taken to ensure that the verniercalipers are pressed against the prepreg or the substrate so that thethickness does not vary. Particularly in the case of the substrate, ifthere is a concern that, even with the vernier calipers pressed againstthe substrate, the measurement error during measurement is overly large,then a photograph is preferably taken of the substrate cross section andenlarged, so that measurements can be conducted with minimal error. Inaddition, in those cases where a substrate is bonded to both surfaces ofthe prepreg, the sum of the individual thickness values for the twosubstrates is used as the thickness value (B).

(Substrate Construction)

Suitable examples of the material used for forming the substrate includefibrous thermoplastic resins and reinforcing fibers. The use of fibrousthermoplastic resins is preferred as it enables an improved interlayerreinforcement effect to be achieved when layers of the intermediatematerial for FRP molding are laminated. Suitable examples of suchmaterials include nylon, polyester, polyethylene, and polypropylene, andprovided a deaerating circuit can be ensured, the material may be anet-like material, a material in which rods or fibers of thethermoplastic resin are aligned unidirectionally, or a laminatedmaterial in which these materials are overlaid at different angles.However, in order to best ensure an efficient deaerating circuit, thethermoplastic resin is most preferably in the form of a fibrousmaterial, and suitable materials include woven fabrics formed fromfibers, as well as materials in which the fibers are alignedunidirectionally and non-woven fabrics. Of these, non-woven fabrics areparticularly desirable as they offer ready formation of the deaeratingcircuit.

Furthermore, the material for the substrate can also usenon-thermoplastic resin fibers, and reinforcing fibers are particularlyfavorable. In those cases where reinforcing fibers are used as thematerial for the substrate, the same reinforcing fibers that were usedto form the prepreg can be used, although different fibers may also beused.

In those cases where the same reinforcing fibers as those used in theprepreg are used, the substrate can be bonded to the prepreg so that theangle of alignment of the reinforcing fibers in the substrate matchesthe angle of alignment of the reinforcing fibers in the prepreg.However, bonding the two together so that the respective angles ofalignment are different enables the lamination step duringquasi-isotropic lamination or the like to be conducted with greaterease, and is consequently preferred. Quasi-isotropic lamination involveslaminating layers with the angles of alignment set to [−45°/0°/45°/90°],so that overall, the FRP is isotropic and displays no anisotropy interms of the FRP properties.

On the other hand, different reinforcing fibers from those used in theprepreg can be used for forming the substrate. In such cases, a hybridFRP can be produced with considerable ease, which is ideal. For example,an FRP produced using an intermediate material in which glass fiber isused as the reinforcing fibers for forming the prepreg, and carbon fiberis used as the reinforcing fibers for forming the substrate becomes aglass/carbon fiber hybrid FRP, enabling optimal design of the costperformance balance. In this case, as was described above, therespective angles of alignment of the reinforcing fibers of thesubstrate and the reinforcing fibers of the prepreg may be either thesame or different.

(Molding Using Prepregs or Intermediate Materials for FRP MoldingAccording to the Present Invention)

When a FRP is produced using either a prepreg or an intermediatematerial for FRP molding according to the present invention, vacuum bagmolding is the most preferred process, although molding using anautoclave or press molding can also be used.

In a process for producing FRP according to the present invention,primary curing is preferably conducted for at least 10 minutes at aprimary curing temperature of no more than 150° C., and then the curingis preferably completed at a temperature equal to, or greater than, theprimary curing temperature. Processes in which the primary curing isconducted at a temperature of no more than 100° C. are particularlypreferred as a resin mold can be used instead of a metal mold, andheating can be conducted using solely steam, which provide significantcost reductions.

In addition, following the primary curing and subsequent removal fromthe mold, the product is preferably subjected to further curing at atemperature either equal to, or higher than, the primary curingtemperature, thus enabling a further reduction in the high-temperaturemolding time.

A prepreg or intermediate material for FRP molding according to thepresent invention provides a deaerating circuit during molding, meaningair from the voids can be guided out through the deaerating circuit andexpelled outside the FRP, thus making these materials ideally suited tovacuum bag molding and oven molding.

Regardless of whether or not oven molding is used, when molding isconducted using a prepreg or an intermediate material for FRP moldingaccording to the present invention, the prepreg or FRP moldingintermediate material is preferably laminated, and then placed under avacuum, so that the air contained within the prepreg or FRP moldingintermediate material can be completely removed before the temperatureis raised. Specifically, a degree of vacuum of no more than 600 mmHg ispreferred, and a degree of vacuum of no more than 700 mmHg is even moredesirable. If the temperature is raised before satisfactory deaeratinghas been completed, then the viscosity of the matrix resin may fall toofar, causing the deaerating circuit to become undesirably blocked beforethe air within the prepreg or FRP molding intermediate material has beencompletely removed. Furthermore, if the process atmosphere is returnedto normal pressure in the middle of the molding process, then there is adanger that air that has already been removed may penetrate back intothe interior of the prepreg or FRP molding intermediate material, and asa result, the vacuum is preferably maintained throughout the moldingprocess.

In addition, when molding is conducted using a prepreg or anintermediate material for FRP molding according to the presentinvention, the structure is preferably held for at least 1 hour, priorto curing, and while the viscosity of the matrix resin is no more than10,000 poise, before the curing step is conducted. During this holdingperiod, the matrix resin can migrate, making it easier to force the airout of the molded product. Holding the structure while the viscosity ofthe matrix resin is no more than 5000 poise before the curing step iseven more desirable. Furthermore, holding the structure in this statefor at least 2 hours before curing is also particularly preferred.

A preferred process for molding a FRP using either a prepreg or a FRPmolding intermediate material according to the present inventioninvolves raising the temperature from a temperature at least 20° C.below the molding temperature to the molding temperature at a rate of nomore than 1° C./minute. The raising of the temperature is initiated oncethe vacuum has been established, and is conducted with the vacuum statemaintained, although during the temperature raising step, if the resinstarts to move very suddenly, then small quantities of residual air canbecome trapped in the cured product under vacuum conditions, namely,under reduced pressure conditions of no more than 50 Torr, and thistrapped air can cause residual interlayer voids and surface pinholes.

Consequently, it is very important to control the speed of movement ofthe resin during the temperature raising step, to ensure that any lastsmall quantities of residual air are expelled from the molded product.In order to achieve this aim, the rate of temperature increase can bekept low, although at very low temperatures, the viscosity of the matrixresin is high, and the movement of the air is too slow, meaning anextremely long time would be required for the matrix resin to impregnateright into the corners of the sheet-like reinforcing fiber substrate,causing a problematic deterioration in productivity.

Because the viscosity of the resin reaches its minimum value neartypical molding temperatures, slowing the rate of temperature increaseto no more than 1° C./minute from a temperature at least 20° C. belowthe molding temperature produces a favorable effect, and is consequentlypreferred. Lowering the rate of temperature increase to no more than 1°C./minute from a temperature at least 30° C. below the moldingtemperature is even more preferred, and lowering the rate from atemperature at least 40° C. below the molding temperature isparticularly desirable. Furthermore, slowing the rate of temperatureincrease to no more than 0.7° C./minute is even more preferred, and tono more than 0.5° C./minute is particularly desirable.

Furthermore, when prepregs or FRP molding intermediate materialsaccording to the present invention are laminated, then in those caseswhere the upper and lower surfaces of the prepregs or FRP moldingintermediate materials can be obviously distinguished, arranging thelayers with the same surface of each layer facing in the same directionenables a more reliable establishment of the deaerating circuit, and isconsequently preferred.

EXAMPLES

In the series of examples 1 to 7 and comparative examples 1 to 3described below, a matrix resin was prepared by uniformly mixing theresin constituents described below. The mixing conditions were asfollows. All of the components except for DICY7 and DCMU99 were mixeduniformly in a kneader set to 100° C., and the temperature of thekneader was then lowered to 50° C., the DICY7 and DCMU99 were added, andmixing was continued to generate a uniform mixture.

<Matrix Resin Composition>

Epikote 828 (a bisphenol A epoxy resin, manufactured by Japan EpoxyResins Co., Ltd.) 40 parts by mass

Epikote 1001 (a bisphenol A epoxy resin (solid at room temperature),manufactured by Japan Epoxy Resins Co., Ltd.) 40 parts by mass

Epiclon N740 (a phenol novolac epoxy resin, manufactured by DainipponInk and Chemicals, Incorporated) 20 parts by mass

DICY7 (dicyandiamide, manufactured by Japan Epoxy Resins Co., Ltd.) 5parts by mass

DCMU99 (3,4-dichlorophenyl-N,N-dimethylurea, manufactured by HodogayaChemical Co., Ltd.) 5 parts by mass

Furthermore, the materials used in each of the examples and comparativeexample, and the methods used for evaluation are described below.

<Short Fibers of Thermoplastic Resin>

Nylon 12 was subjected to melt spinning to generate a short fiber with asize of 200 tex, and these fibers were then cut to a length of 5 mm tocomplete preparation of the short fibers. Hereafter, these are referredto simply as short fibers.

<Compressive Strength after Impact>

Measurement of the compressive strength after impact was measured inaccordance with the SACMA recommended method SRM2-88, and involvedmeasuring the compressive strength following application of a 270 lb-inimpact.

<Method of Measuring Tg>

Using a RDA-700 device manufactured by Rheometrics Inc., or aviscoelastic spectrometer with equivalent functionality, the temperaturewas raised from approximately 0° C. at a rate of 2° C./minute, and thedynamic modulus of elasticity (G′) of the sample was measured. Theresults of the measurements were graphed with temperature along thehorizontal axis and logarithm of G′ along the vertical axis as shown inFIG. 8, a tangent L1 was drawn from the glass region and another tangentL2 was drawn from the transition region, and the temperaturecorresponding with the point of intersection C of the two tangents wasused as Tg (see FIG. 8).

<Minimum Viscosity>

Using a dynamic analyzer (RDA-200) manufactured by Rheometrics, Inc.,viscosity measurements were conducted from room temperature (23° C.) to150° C. using a rate of temperature increase of 5° C./minute and anangular velocity of 10 rad/second. The lowest value observed for theviscosity during this test was recorded as the minimum viscosity for theresin composition.

<Surface Coverage Ratio>

A smooth and transparent polyethylene film of thickness 20 μm was bondedto a sea-and-island-type patterned surface of a prepreg by applicationof a metal heated roll press under conditions including a temperature of40° C., a pressure of 1 atom, and a roll speed of 5 m/minute. Thesurface was then photographed using a CCD camera of at least 2megapixels, and an image analysis system (detailed fine image analysis“IP1000”) manufactured by Asahi Engineering Co., Ltd. was used todetermine the surface area covered by the thermosetting resin, bymeasuring the surface area of those regions where the thermosettingresin had stuck to the polyethylene film causing a change in coloring,and the ratio of this surface area relative to the total surface area ofthe prepreg was then used to determine the surface coverage ratio.

<Island Portions Weave Intersection Coverage Ratio>

In the same manner as described above for the measurement of the surfacecoverage ratio, a smooth and transparent polyethylene film of thickness20 μm was bonded to a prepreg by application of a metal heated rollpress under conditions including a temperature of 40° C., a pressure of1 atm, and a roll speed of 5 m/minute. The coated prepreg was then cutinto a 10 cm×10 cm square, the surface of the prepreg to which thepolyethylene film had been bonded was photographed using a CCD camera,and the aforementioned image analysis system was used to determine thenumber of individual regions (T: the number of islands) where thethermosetting resin had stuck to the polyethylene film causing a changein coloring.

Subsequently, the polyethylene film was peeled off, the surface of theprepreg was photographed again with the CCD camera, and an imageanalyzer was used to measure the number of weave intersections (Y)within the reinforcing fiber woven fabric on thesea-and-island-patterned surface. The island portions weave intersectioncoverage ratio was then calculated from the formula (1).

<Evaluation of FRP External Appearance (for the Existence of Pinholes)>

Using the method described below, a piece of chalk was pressed againstthe surface of the produced flat sheet of FRP and used to coat theentire surface of the sheet. The surface was then wiped lightly with adry cloth or the like, making any pinholes very visible, and enabling anevaluation of whether or not any pinholes exist.

<Evaluation of FRP Voids>

Following evaluation for pinholes, the flat sheet of FRP was cut throughthe center in a direction perpendicular to the thickness direction, andthe cross section was photographed at 20× magnification. An evaluationof whether or not any voids exist was then made by inspecting the crosssection photograph.

<Evaluation of Tackiness>

Under an atmosphere at a temperature 23° C. and a humidity of 50%, asteel plate of thickness 2 mm that had been treated with a releasingagent was stood up vertically with respect to the ground, and a prepregthat had been cut to a size of 10 cm×10 cm was stuck to the surface ofthe steel plate. If the prepreg remained attached to the steel platewith no signs of peeling after 1 minute, then the surface tackiness ofthe prepreg was adjudged to be favorable.

Example 1

The matrix resin was applied uniformly to a release sheet at a resinweight of 430 g/m², thus forming a resin film. This resin film wassupplied to a piece of carbon fiber cloth TRK510, manufactured byMitsubishi Rayon Co., Ltd. (fiber weight 646 g/m², 2/2 twill) from thebottom surface of the cloth, thus impregnating the carbon fiber clothwith the resin. The temperature during impregnation vas 60° C., and thepressure was adjusted to complete the preparation of a prepreg. When theresin impregnation ratio of the thus produced prepreg was measured, theresult was 90%, thus confirming the prepreg as conforming to the presentinvention.

Next, using the release sheet side of the thus produced prepreg of thepresent invention as the tool side (a stainless steel plate), a 4-plylaminate was formed at 0° C. The layers from the second layer up werearranged so that the release sheet side of the prepreg faced theopposite side of the previous layer. Vacuum bag molding was conducted,and a 30 cm square panel was subjected to oven molding. The operation oflaminating the prepregs presented absolutely no problems.

The molding conditions used for the prepreg laminate were as follows.Namely, the temperature was raised from room temperature to 50° C. at arate of 3° C./minute, the laminate was then held at 50° C. for 30minutes under reduced pressure at 20 Torr to allow deaerating, andsubsequently, with the reduced pressure state maintained at 20 Torr, thetemperature was raised to 120° C. at a rate of 1° C./minute. Thetemperature was then held at 120° C. for 1 hour, thus yielding a 30 cmsquare panel.

The thus obtained panel had no surface voids, and when the panel was cutthrough the center and the resulting cross section was inspected, nointernal voids were visible.

Comparative Example 1

With the exception of altering the impregnation temperature to 70° C., aprepreg was prepared in the same manner as the example 1. When thecross-section of the prepreg was inspected, it was found that the resinhad migrated right through to the opposite surface from the releasesheet, producing a resin impregnation ratio of 100%. This prepreg wasthen laminated, and a panel was molded in the same manner as theexample 1. The operation of laminating the prepregs presented absolutelyno problems, but the surface of the molded panel contained pinholes.Furthermore, when a central cross section of the panel was inspected inthe same manner as the example 1, a plurality of internal voids wasobserved.

Comparative Example 2

A resin film was prepared in the same manner as the example 1, and aprepreg was then formed. However, the impregnation of the carbon fibercloth with the resin was conducted at room temperature, with onlypressure being applied. Almost no impregnation occurred, and absolutelyno resin was visible at the opposite surface to where the resin wassupplied. When the resin impregnation ratio of the thus produced prepregwas measured, the result was 30%. This prepreg was then laminated, and apanel was molded in the same manner as the example 1. The lamination wasconducted with the release sheet side of the prepregs facing the toolsurface.

A small number of pinholes were identified in the surface of the thusproduced panel, and when a central cross section of the panel wasinspected in the same manner as the example 1, internal voids were alsoobserved.

A piece of carbon fiber cloth TR3110 (number of filaments 3000, plainweave, weight 200 g/m², manufactured by Mitsubishi Rayon Co., Ltd.) wasimpregnated with the same resin composition as that used in the example1, thus forming a prepreg of the present invention. When the resinimpregnation ratio was measured, the result was 70%. A 16-ply laminateof this prepreg was formed using an alignment pattern of[0°/45°/90°/−45°/0°/45°/90°/−45°/−45°/90°/45°/0°/−45°/90°/45°/0°], and a1 m square panel was molded. The lamination was conducted with therelease sheet side of the prepregs facing the tool surface. Theoperation of laminating the prepregs presented absolutely no problems.

Under the molding conditions used, the temperature was raised from roomtemperature to 45° C. at a rate of 5° C./minute, the laminate was thenheld at 45° C. for 60 minutes under reduced pressure at 7 Torr to allowdeaerating, and subsequently, the temperature was raised to 80° C. at arate of 2° C./minute, and from 80° C. to 120° C. at a rate of 0.7°C./minute. The temperature was then held at 120° C. for 1 hour, thusyielding a 1 m square panel.

The thus obtained panel had no surface pinholes, and when the interiorwas inspected in the same manner as the example 1, no internal voidswere visible.

Example 4

An epoxy resin composition #830 manufactured by Mitsubishi Rayon Co.,Ltd. was used as the matrix resin. Using this resin, a resin film wasprepared in the same manner as the example 1, and this was thenimpregnated into a TRK510. The impregnation temperature was set to 50°C. When the resin impregnation ratio of the thus obtained prepreg wasmeasured, the result was (60%, thus confirming the prepreg as conformingto the present invention. Using this prepreg, a molded product wasmolded. A wooden female mold was used as the molding die. An 8-plylaminate was formed using an alignment pattern of[0°/45°/90°/−45°/−45°/90°/45°/0°], with the release sheet side of theprepreg facing the tool surface, and subsequently prepregs arranged sothat the release sheet side faced the opposite side of the previouslayer. The operation of laminating the prepregs presented absolutely noproblems.

Under the molding conditions used, the temperature was raised from roomtemperature to 45° C. at a rate of 2° C./minute, the laminate was thenheld at 45° C. under reduced pressure at 2 Torr for 4 hours to allowdeaerating, and subsequently, the temperature was raised to 80° C. at arate of 0.5° C./minute. The temperature was then held at 80° C. for 2hours, thus yielding a molded product.

The thus obtained molded product had no surface pinholes, and when theproduct was cut open and the exposed cross section was inspected, nointernal voids were visible.

Example 5

Using the resin used in the example 1, and using a non-crimped fabricQuadraxial-Carbon-Gelege (+45°: Carbon 267 g/m², 0°: Carbon 268 g/m²,−45°: Carbon 267 g/m², 90°: Carbon 268 g/m², stitching: PES 6 g·m²,weight 1076 g/m²) manufactured by Saertex Co., Ltd. as a sheet-likereinforcing fiber substrate, a prepreg was prepared in the same manneras the example 1. However, the resin weighting was 717 g/m². When theresin impregnation ratio was measured, the result was 75%, thusconfirming the prepreg as conforming to the present invention. A 2-plylaminate was prepared with the prepreg surfaces facing in the samedirection, and a FRP was then molded. The molding was conducted underthe same molding conditions as the example 1. The thus obtained moldedproduct displayed no internal voids and no surface pinholes.

Example 6

8.1 parts by mass of the short fibers were added to 100 parts by mass ofthe thermosetting resin, and then mixed uniformly in a kneader at 50°C., thus yielding a thermosetting resin composition.

Using a roll coater, this resin composition was applied to a releasesheet with a resin weight of 133 g/m². This resin film was supplied atroom temperature to one surface of a piece of carbon fiber cloth TR3110,a sheet-like reinforcing fiber substrate manufactured by MitsubishiRayon Co., Ltd. (fiber weight 200 g/m², plain weave), and a prepreg ofthe present invention was prepared by heating to 40° C., applyingpressure from a roller, and ensuring that the resin did not migrate fromthe supply surface right through to the opposite surface. When the resinimpregnation ratio of the thus produced prepreg was measured, the resultwas 60%.

A 24-ply laminate of this prepreg was formed with the fiber alignmentdirection (of the warp) set to[45°/0°/−45°/90°/45°/0°/−45°/90°/45°/0°/−45°/90°/90°/−45°/0°/45°/90°/−45°/0°/45°/90°/−45°/0°/45°],and oven molding was used to mold a 500 mm×500 mm panel. Under themolding conditions used, following lamination of the prepregs, thelaminate was first placed under vacuum, and was then heated for 2 hoursat 50° C., and then a further 2 hours at 80° C., before being returnedto normal pressure and held for 1 hour at 130° C., thus yielding a CFRPpanel. The rate of temperature increase used was 0.5° C./minute, and therate of cooling following the 1 hour at 130° C. was 2° C./minute.

The thus obtained CFRP panel had no pinholes and displayed an extremelyfavorable external appearance. Furthermore, when the panel was cutthough the center, no internal voids were visible. When a test specimenwas cut from the panel and the compressive strength after impact wasmeasured, the result was an extremely high 262 MPa.

Comparative Example 3

A prepreg was prepared in the same manner as the example 6. However,during the step for integrating the resin film with the sheet-likereinforcing fiber substrate, the level of impregnation was increased, sothat almost no non-impregnated portions remained on the opposite surfaceto the surface from which the resin was supplied. The resin impregnationratio was 100%.

The thus obtained prepreg was laminated and molded in the same manner asthe example 6, yielding a CFRP panel. This CFRP panel displayedpinholes, and the external appearance was poor. Furthermore, when thepanel was cut through the center, a plurality of internal voids wasvisible. When the compressive strength after impact was measured forthis panel, the result was low, and 222 MPa.

Example 7

With the exception of using a unidirectional, sheet-like reinforcingfiber substrate (with a fiber weight of 200 g/m²) forstitching-reinforcement formed by stitching unidirectionally alignedTR50S-12L fibers with polyester fiber, a prepreg of the presentinvention was formed in exactly the same manner as the example 6. Theresin impregnation ratio of the thus obtained prepreg was 45%.

The thus obtained prepreg was laminated and molded in the same manner asthe example 6, yielding a CFRP panel. When the panel was cut through thecenter, no internal voids were visible. When the compressive strengthafter impact was measured for this panel in the same manner as theexample 6, the result was a very high 325 MPa.

Comparative Example 4

A prepreg was prepared in the same manner as the example 7. However,during the step for integrating the resin film with the sheet-likereinforcing fiber substrate, the level of impregnation was increased, sothat resin exuded from the opposite surface to the surface from whichthe resin was supplied. The resin impregnation ratio was 100%.

The thus obtained prepreg was laminated and molded in the same manner asthe example 7, yielding a CFRP panel. When this panel was cut throughthe center, internal voids were visible. When the compressive strengthafter impact was measured for this panel in the same manner as theexample 6, the result was 283 MPa, considerably lower than that observedfor the example 7.

Example 8

(A) A carbon fiber cloth TRK510 (fiber weight 646 g/m², 2/2 twill,thickness 355 μm), manufactured by Mitsubishi Rayon Co., Ltd., was usedas the sheet-like reinforcing fiber substrate, and

(B) an epoxy resin #830, manufactured by Mitsubishi Rayon Co., Ltd.,which can be cured by heating at 80° C. for 2 hours, was used as acurable resin composition.

The curable resin composition (B) was applied to a release sheet with aresin weight of 175 g/m². One of these release sheets was then bonded toboth the top and bottom surfaces of the sheet-like reinforcing fibersubstrate (A), with both of the curable resin composition surfacesfacing inwards. The bonding was conducted at room temperature, with thetackiness of the curable resin composition (B) used to effect thebonding. When the thus obtained FRP molding intermediate material of thepresent invention was cut open and the interior was inspected, it wasfound that the portions into which the curable resin composition had notimpregnated existed as a continuous portion.

A 10-ply laminate of the thus produced prepreg of the present inventionwas prepared, with the prepregs aligned in the same direction, and a 800mm×800 mm CFRP panel was molded. Under the molding conditions used,atmospheric pressure was first confirmed as having fallen to no morethan 700 mmHg, and the temperature was then raised from room temperatureat a rate of 1° C./minute, and held at 50° C. for 3 hours, before thetemperature increase was resumed and heating was continued at 80° C. for2 hours, thus curing the laminate. The viscosity of the #830 resin at50° C., measured using a DSR200 device manufactured by Rheometrics,Inc., with a rate of temperature increase of 2° C./minute, was 3500poise.

The surface of the produced CFRP panel displayed absolutely no pinholes.Furthermore, when the FRP panel was cut though the center and the cutcross section was inspected, no internal voids were visible.

Comparative Example 5

A prepreg was prepared using the same material as the example 8.However, the resin was applied at a weight of 350 g/m², and was bondedto only one surface of the sheet-like reinforcing fiber substrate (A).The thus obtained FRP molding intermediate material was molded in thesame manner as the example 1, thus yielding a FRP panel.

Although no pinholes were observed in the surface of the produced CFRPpanel, when the panel was cut though the center and the cut crosssection was inspected, a plurality of small internal voids was visible.

Comparative Example 6

A prepreg was prepared using the same material as the example 8. Theresin was applied at a weight of 175 g/m² in the same manner as theexample 8, but rather than simply bonding the resin to both surfaces ofthe sheet-like reinforcing fiber substrate (B), the structure was passedtwice through a fusing press under conditions of 60° C., 0.1 MPa, and aspeed of 25 cm/minute, thus ensuring good impregnation. When the thusproduced prepreg was cut though the center and the cut cross section wasinspected, the curable resin composition had impregnated right into thecenter of the substrate, and although a few portions with no curableresin composition were visible, each of these non-impregnated portionswas partitioned off by the curable resin composition.

The produced prepreg was molded in the same manner as the example 8,yielding a FRP panel, but the surface of the thus obtained FRP panelcontained a plurality of pinholes. Furthermore, when the panel was cutthough the center and the cut cross section was inspected, a largenumber of variously sized internal voids were visible.

Example 9

A prepreg was prepared in the same manner as the example 8. However, anepoxy resin composition that was capable of being cured by heating at80° C. for 2 hours, formed by uniformly mixing the resin componentslisted below at a temperature of 55° C., was used as the curable resincomposition (B), and when this curable resin composition (B) was appliedto the release sheet, a resin weight of 215 g/m² was used.

Epikote 1001 (a bisphenol A epoxy resin (solid at room temperature),manufactured by Japan Epoxy Resins Co., Ltd.) 70 parts by mass

Epiclon N740 (a phenol novolac epoxy resin, manufactured by DainipponInk and Chemicals, Incorporated) 20 parts by mass

Novacure HX3722 (a microcapsule based latent curing agent, manufacturedby Asahi Kasei Corporation) 10 parts by mass

Omicure 94 (an amine based curing agent, manufactured by PTI Japan Co.,Ltd.) 5 parts by mass

Using the thus produced prepreg, a CFRP panel was produced in the samemanner as the example 8. The surface of the produced CFRP paneldisplayed absolutely no pinholes. Furthermore, when the CFRP panel wascut though the center and the cut cross section was inspected, nointernal voids were visible. In addition, when the flexural strength ofthe product CFRP panel was measured in accordance with ASTM D790, a highstrength value of 680 MPa was obtained.

Comparative Example 7

A prepreg was prepared in the same manner as the example 9. However,following bonding of the resin film, the structure was passed twicethrough a fusing press under conditions of 60° C., 0.1 MPa, and a speedof 25 cm/minute, thus ensuring good impregnation. When the thus producedprepreg was cut, and the cut cross section was inspected, the matrixresin had impregnated right into the center of the substrate, andalthough a few portions with no matrix resin were visible, each of thesenon-impregnated portions was partitioned off by the matrix resin, and nocontinuous non-impregnated portion existed.

Using the produced prepreg, a CFRP panel was produced in the same manneras the example 9. The surface of the thus obtained CFRP panel containeda plurality of pinholes. Furthermore, when the panel was cut through thecenter and the cut cross section was inspected, a large number ofvariously sized internal voids were visible. Furthermore, when the CFRPpanel was cut though the center and the cut cross section was inspected,no internal voids were visible. In addition, when the flexural strengthof the product CFRP panel was measured in accordance with ASTM D790, avalue of 420 MPa, which was lower than that observed for the example 9,was obtained.

Example 10

An epoxy resin composition (#340, manufactured by Mitsubishi Rayon Co.,Ltd., minimum viscosity 20 poise) was applied uniformly to a releasesheet wherein one surface thereof is release-treated, using a rollcoater, at a weight of 133 g/m². A carbon fiber woven fabricmanufactured by Mitsubishi Rayon Co., Ltd. (TRK510 (fiber weight: 646g/m²)) was then bonded to the resin composition side of this resinsupport sheet. Another release sheet that had undergonerelease-treatment in the same manner as described above was thenoverlaid on the carbon fiber fabric side such that a release-treatedsurface is provided on the fabric. The resulting structure was thenpressed and heated by passage through a pair of heated rollers at 40°C., thus forming a prepreg.

The thus obtained prepreg had a resin composition surface coverage ratioof 3%, and the weave intersection coverage ratio for the island portionsof the resin composition that existed at the surface was 60%.Furthermore, evaluation of the workability revealed that the prepregdisplayed favorable tackiness, and stuck favorably to a steel plate.

Using this prepreg, a FRP was produced in the manner described below. 10prepreg sheets that had been cut to dimensions of 20 cm long×20 cm widewere laminated. This laminate was provided on a steel base plate(thickness 2 mm), the surface of which had been treated with a releasingagent. Subsequently, a polytetrafluoroethylene film containing holes of2 mm diameter at 10 cm intervals, a nylon cloth of weight 20 g/m², and aglass fiber non-woven fabric of weight 40 g/m² were placed in sequenceon top of the laminate. The resulting structure was then covered andsealed using a nylon film. The space sealed within the outer nylon filmwas then placed under reduced pressure, and while the pressure wasmaintained at no more than 600 mmHg, the temperature was raised fromroom temperature to 130° C. at a rate of 2° C./minute, and was then heldat 130° C. for 2 hours, thus yielding a FRP.

When the thus produced FRP was subjected to the evaluations describedabove, it was found that the surface on the base plate side of themolded FRP had a favorable external appearance with no pinholes, and across section photograph revealed no visible interlayer or intralayervoids.

Examples 11 to 14

Using the same resin composition and reinforcing fiber woven fabric asthose used in the example 10, a series of fiber-reinforced fabricprepregs with the respective surface coverage ratios shown in Table 1were prepared by conducting a plurality of repetitions of pressing andheating with a roller heated to 40°. Each of the prepregs had an islandportions weave intersection coverage ratio of 60%.

Evaluation of these prepregs in the same manner as the example 10revealed that all of the prepregs had favorable handling properties, andthe produced FRPs all had favorable external appearances, and no voids.

Examples 15 and 16

Prepregs were prepared in the same manner as the example 11, but withthe conditions altered to produce a resin composition surface coverageratio of 40%. The number of repetitions of the impregnation step usingthe heated roll press was adjusted to produce island portions weaveintersection coverage ratios of 100% and 50% respectively. Evaluation ofthese prepregs in the same manner as the example 10 revealed that bothof the prepregs had favorable handling properties, and the produced FRPsboth had favorable external appearances, and also displayed nointerlayer or intralayer voids.

Examples 17 to 21

With the exceptions of altering the temperature during impregnation to60° C. in the case of the example 17, increasing the minimum viscosityof the epoxy resin composition as shown in Table 2 in the case of theexamples 18 and 19, and altering the weight of the carbon fiber fabricas shown in Table 2 in the case of the examples 20 and 21, prepregs wereprepared in the same manner as the example 10. All of the prepregsdisplayed favorable tackiness, and the produced FRPs all had favorableexternal appearances, and displayed no voids.

Examples 22 and 23

With the exceptions of altering the minimum viscosity to 1100 poise inthe case of the example 22, altering the fiber weight to 1600 g/m² inthe case of the example 23, and setting the other values as shown inTable 2, prepregs were prepared in the same manner as the example 10.The tackiness of these prepregs was good. On the other hand, the FRPsproduced from these prepregs did contain internal voids, although FRPswith no pinholes were obtained.

Example 24

With the exception of applying the resin composition on the releasesheet with a uniform weighting per unit of surface area of 266 g/m²,preparation was conducted in the same manner as the example 10, up toand including the heating and pressing using a pair of heated rollers.The resin support sheet was then peeled off, TR3110 was bonded to thesame surface, and then a similar release sheet to that described abovewas overlaid on the side of the just bonded TR3110. The resultingstructure was then pressed and heated again by passage through the pairof heated rollers at 40° C., and the overlaid release sheet was peeledoff, yielding a prepreg in which both sides displayed asea-and-island-pattern.

The surface coverage ratio of the thus obtained prepreg, totaled acrossboth surfaces, was 50%, and the island portions weave intersectioncoverage ratio was 60%. This prepreg also stuck favorably to a steelsheet, and was adjudged to have a good level of tackiness. Furthermore,when this prepreg was used to conduct the molding evaluations describedabove, the molded FRP had a favorable external appearance with nosurface pinholes, and no internal voids were observed.

Comparative Examples 8 to 10

With the exceptions of altering the surface coverage ratios, the islandportions weave intersection coverage ratios, and the fiber weights tothe values shown in Table 3, prepregs were prepared in the same manneras the example 9 and then evaluated. The evaluation results showed thatthe comparative example 8, which had a lower surface coverage ratio thanthe example 10, displayed only weak tackiness, and had poor handlingproperties. In contrast, the comparative example 9, which had an overlyhigh surface coverage ratio when compared with the example 10, and thecomparative example 10, which had a lower island portions weaveintersection coverage ratio than the example 10, produced moldedproducts with pinholes and interlayer voids, meaning products withsatisfactory external appearances and mechanical characteristics couldnot be obtained.

A thermosetting resin composition acetone solution used in the examples25 to 30 and the comparative examples 11 to 14 employed an acetonesolution containing 60% by mass of the epoxy resin composition, and wasprepared by dissolving an epoxy resin composition (solid at roomtemperature), comprising the constituents listed below, in acetone togenerate a homogenous solution (hereafter referred to simply as theepoxy solution).

<Epoxy Resin Composition>

Epikote 828 (a bisphenol A epoxy resin (liquid at room temperature),manufactured by Japan Epoxy Resins Co., Ltd.) 50 parts by mass

Epikote 1004 (a bisphenol A epoxy resin (solid at room temperature),manufactured by Japan Epoxy Resins Co., Ltd.) 30 parts by mass

Epiclon N740 (a phenol novolac epoxy resin, manufactured by DainipponInk and Chemicals, Incorporated) 20 parts by mass

DCMU99 (3,4-dichlorophenyl-N,N-dimethylurea, manufactured by HodogayaChemical Co., Ltd.) 5 parts by mass

Example 25

A carbon fiber woven fabric Pyrofil TRK510 that used carbon fiber forboth the warp and the woof (manufactured by Mitsubishi Rayon Co., Ltd.,2/2 twill fabric, fiber weight 646 g/m², thickness 0.57 mm) wasimpregnated by immersion in the epoxy solution, and was then dried bywarm air drying at 40° C. to remove the solvent, thus yielding a prepregwith a resin content of 46.7% by mass (a resin weight of 564 g/m²). Whenthe thickness of the prepreg was measured with vernier calipers, themeasured thickness (A) was 0.85 mm. Using a carbon fiber woven fabricPyrofil TR3110 that used carbon fiber for both the warp and the woof(manufactured by Mitsubishi Rayon Co., Ltd., plain weave, fiber weight200 g/m², thickness (B)=0.23 mm) as a substrate, the substrate wasbonded to one surface of the prepreg so that the warp and woof werealigned in the same direction as in the prepreg, thus forming anintermediate material for FRP molding. This intermediate materialdisplayed a (B)/(A) ratio of 0.27, the overall fiber weight of theentire intermediate material was 846 g/m², and the resin content was 40%by mass.

The prepreg side surface of the thus obtained FRP molding intermediatematerial was stuck to a molding die, and a 3-ply laminate was thenformed by overlaying the intermediate materials with the same angle ofalignment and the same surfaces facing the same direction, and the thusformed 500 mm×500 mm flat sheet was then subjected to oven molding. Themolding conditions were as follows. Namely, under a vacuum of no morethan 5 Torr, the temperature was raised from room temperature to 50° C.at a rate of 3° C./minute, held at 50° C. for 3 hours, and then raisedto 120° C. at a rate of 0.5° C./minute, and subsequently held at 120° C.for 2 hours, thus yielding a FRP panel.

Despite being formed by oven molding, as shown in Table 4, the thusobtained FRP panel displayed no surface pinholes, and when the FRP panelwas cut through the center and the interior was inspected, no internalvoids were visible.

Example 26

With the exceptions of altering the resin content to 57.1% by mass (aresin weight of 861 g/m²) and setting the thickness (A)=1.1 mm, aprepreg was prepared in the same manner as the example 25. Using areinforcing fiber woven fabric (TRK510, thickness (B)=0.57 mm) as asubstrate, which is same with those used in the prepreg, the substratewas bonded to one surface of the prepreg, with the direction ofalignment of the reinforcing fibers inclined 45° relative to that of theprepreg, thus forming an intermediate material for FRP molding. Thisintermediate material displayed a (B)/(A) ratio of 0.52, the overallfiber weight of the entire intermediate material was 1292 g/m², and theresin content was 40% by mass.

The thus obtained FRP molding intermediate material was laminated withthe angle of alignment of the warp fibers set to[−45°/0°/45°/90°/90°/45°/0°/−45°], and was then oven molded in the samemanner as the example 24, yielding a FRP panel. In this example, becausethe intermediate material was a 0°/45° double layered structure, a 4-plylaminate of intermediate material units was formed.

As shown in Table 4, the thus obtained FRP panel displayed no surfacepinholes, and when the FRP panel was cut through the center and theinterior was inspected, no internal voids were visible.

Example 27

With the exceptions of replacing the TRK510 with roving glass clothWR800 manufactured by Nitto Boseki Co., Ltd., and altering the resincontent to 53.3% by mass (a resin weight of 450 g/m²) and the thickness(A)=0.71 mm, a prepreg was prepared in the same manner as the example25. A sheet of Pyrofil TR3110 was then bonded to one surface of theprepreg so that the warp and woof were aligned in the same direction asin the prepreg, thus forming a glass fiber/carbon fiber hybrid FRPmolding intermediate material ((B)/(A)=0.32).

A 4-ply laminate was then formed by overlaying the thus obtainedintermediate material with the same angle of alignment and the samesurfaces facing the same direction, and the laminate was then subjectedto oven molding in the same manner as the example 25, yielding a glassfiber/carbon fiber hybrid FRP. By using an intermediate material of thepresent invention, a hybrid FRP was able to be molded with considerableease.

As shown in Table 4, the thus obtained FRP panel displayed no surfacepinholes, and when the FRP panel was cut through the center and theinterior was inspected, no internal voids were visible.

Example 28

With the exceptions of altering the resin content to 51.9% by mass (aresin weight of 697.5 g/m²), and setting the thickness (A)=0.96 mm, aprepreg was prepared in the same manner as the example 25. Using PyrofilTR3110 as the substrate, substrates were bonded to both the upper andlower surfaces of the prepreg so that the warp and woof were aligned inthe same direction as in the prepreg, thus yielding an intermediatematerial for FRP molding. This intermediate material displayed a (B)/(A)ratio of 0.24, the overall carbon fiber weight of the entireintermediate material was 1064 g/m², and the resin content was 40% bymass.

A 10-ply laminate was then formed by overlaying the thus obtainedintermediate material of the present invention, with the same angle ofalignment and the same surfaces facing the same direction, and thelaminate was then subjected to oven molding in the same manner as theexample 25, yielding a FRP panel.

As shown in Table 4, the thus obtained FRP panel displayed no surfacepinholes, and when the FRP panel was cut through the center and theinterior was inspected, no internal voids were visible.

Example 29

With the exceptions of replacing the epoxy resin with a phenol resinmethanol solution Phenolite 5900 (approximately 60% by mass)manufactured by Dainippon Ink and Chemicals, Incorporated, and alteringthe resin content to 57.1% by mass (a resin weight of 861 g/m²) and thethickness (A)=1.1 mm, a prepreg was prepared in the same manner as theexample 25. A sheet of Pyrofil TR3110 was then bonded to one surface ofthe prepreg so that the carbon fibers were aligned in the same directionas in the prepreg, thus yielding an intermediate material for FRPmolding. This intermediate material displayed a (B)/(A) ratio of 0.21,the overall carbon fiber weight of the entire intermediate material was1292 g/m², and the resin content was 40% by mass.

A 3-ply laminate was then formed by overlaying the thus obtainedintermediate material with the same alignment, and the resulting 1000mm×1000 mm FRP panel was then subjected to oven molding. The molding wasconducted under a vacuum of no more than 5 Torr, and the temperature wasraised from room temperature to 90° C. at a rate of 0.5° C./minute, andthen held at 90° C. for 20 hours.

As shown in Table 4, the thus obtained FRP panel displayed no surfacepinholes, and when the FRP panel was cut through the center and theinterior was inspected, no internal voids were visible.

Comparative Example 11

This comparative example presents an example in which a substrate is notbonded to the prepreg. With the exceptions of setting the resin contentto 40.0% (a resin weight of 431 g/m²), and the thickness (A)=0.73 mm, aprepreg was prepared in the same manner as the example 25.

Without bonding any substrates, an 8-ply laminate was formed using onlythe prepreg, with the prepreg alignments set to[−45°/0°/45°/90°/90°/45°/0°/−45°], and the resulting laminate was thensubjected to oven molding in the same manner as the example 24, thusyielding a FRP panel.

As shown in Table 4, the thus obtained FRP panel contained a pluralityof surface pinholes, and when the FRP panel was cut through the centerand the interior was inspected, a plurality of internal voids was alsovisible.

Comparative Example 12

With the exceptions of altering the resin content to 40.5% (a resinweight of 430 g/m²), and the thickness (A)=0.74 mm, a prepreg wasprepared in the same manner as the example 25. A sheet of glass clothH20 F5 104 (thickness (B)=0.04 mm) manufactured by Unitika Glass FiberCo., Ltd. was then bonded to the prepreg as the substrate, yielding anintermediate material for FRP molding. This intermediate materialdisplayed a (B)/(A) ratio of 0.05.

This FRP molding intermediate material was subjected to oven molding inthe same manner as the example 25, yielding a FRP panel. As shown inTable 4, the thus obtained FRP panel contained surface pinholes, andwhen the FRP panel was cut through the center and the interior wasinspected, internal voids were also visible.

Comparative Example 13

With the exceptions of altering the resin content to 32.0% (a resinweight of 300 g/m²), and the thickness (A)=0.62 mm, a prepreg wasprepared in the same manner as the example 25. A polyester fibernon-woven fabric (fiber weight 132 g/m², thickness (B)=1.7 mm) wasbonded to the prepreg, yielding an intermediate material for FRPmolding. This intermediate material displayed a (B)/(A) ratio of 2.74.

This FRP molding intermediate material was subjected to oven molding inthe same manner as the example 25, yielding a FRP panel. As shown inTable 4, the surface of thus obtained FRP panel contained a plurality ofresin non-impregnated portions, and when the FRP panel was cut throughthe center and the interior was inspected, a plurality of internal voidswas also visible.

Example 30

Carbon fibers Pyrofil TR50S-12L manufactured by Mitsubishi Rayon Co.,Ltd. were aligned unidirectionally with a fiber weight of 190 g/m², andthe same method as the example 25 was then used to prepare a prepregwith a resin content of 30.2% by mass (a resin weight of 82.3 g/m²), anda thickness (A)=0.18 mm. A non-woven fabric comprising nylon 12 fibers(fiber weight 20 g/m²) with a thickness (B)=0.32 mm was bonded to onesurface of the prepreg, yielding an intermediate material for FRPmolding ((B)/(A)=1.78).

A 24-ply laminate was then formed by overlaying the thus obtained FRPmolding intermediate material with the alignment of the carbon fibersset to [−45°/0°/45°/90°] 3s (wherein, 3s means a laminate produced byrepeating the lamination repeating unit 3 times is then bonded toanother laminate which is a mirror image. In other words, the initial12-ply laminate is arranged with the carbon fiber side facing the die,and the subsequent 12-ply laminate is then arranged with the carbonfiber side facing the opposite direction to the die.) The resultinglaminate was subjected to oven molding in the same manner as the example24, yielding a FRP panel.

The thus obtained FRP panel contained no pinholes in either the surfacesor between the layers, and when the FRP panel was cut through the centerand the interior was inspected, no internal voids were visible. A CAI(residual compressive strength after impact) measurement was performedfor the panel. The CAI measurement was conducted in accordance with theSRM2-88 method of SACMA. The applied impact was 1500 inch-pounds/inch.The result of the CAI measurement on the panel was 350 MPa, a high valuefor a FRP.

Comparative Example 14

With the exceptions of altering the resin content to 35.0% (a resinweight of 102.3 g/m²), and setting the thickness (A)=0.19 mm, a prepregwas prepared in the same manner as the example 25. A 24-ply laminate wasproduced using only the thus obtained prepreg, with the alignment set to[−45°/0°/45°/90°] 3s, and the resulting laminate was subjected to ovenmolding in the same manner as the example 25, thus forming a FRP panel.

The thus obtained FRP panel had a few surface pinholes and interlayervoids, and when the FRP panel was cut through the center and theinterior was inspected, internal voids were also visible. Furthermore,when a CAI measurement was conducted on the panel, the result was acomparatively low 210 MPa.

TABLE 1 Example Example Example Example Example Example Example 10 11 1213 14 15 16 Surface coverage ratio (%) 3 20 40 60 80 40 40 Islandportions weave 60 60 60 60 60 40 100 intersection coverage ratio (%)Minimum viscosity (poise) 20 20 20 20 20 20 20 Fiber weight ofreinforcing 650 650 650 650 650 650 650 fiber fabric (g/m²) Externalappearance No No No No No No No (existence of pinholes) Existence ofvoids No No No No No No No Tackiness Good Good Good Good Good Good Good

TABLE 2 Example Example Example Example Example Example Example Example17 18 19 20 21 22 23 24 Surface coverage ratio (%) 60 60 60 60 60 60 6050 Island portions weave 50 50 50 50 50 60 60 60 intersection coverageratio (%) Minimum viscosity (poise) 20 950 100 500 500 1100 500 20 Fiberweight of reinforcing 650 650 650 50 1500 650 1600 400 fiber fabric(g/m²) External appearance No No No No No No No No (existence ofpinholes) Existence of voids No No No No No Yes Yes No Tackiness GoodGood Good Good Good Good Good Good

TABLE 3 Comparative Comparative Comparative example 8 example 9 example10 Surface coverage ratio (%) 2 81 70 Island portions weave 60 60 35intersection coverage ratio (%) Minimum viscosity (poise) 20 20 20 Fiberweight of reinforcing 650 650 650 fiber fabric (g/m²) Externalappearance No No Yes (existence of pinholes) Existence of voids Yes YesYes Tackiness Poor Good Good

TABLE 4 Example Example Example Example Example Example ComparativeComparative Comparative Comparative 25 26 27 28 29 30 example 11 example12 example 13 example 14 Prepreg TRK510 TRK510 WR800 TRK510 TRK510TR50S- TRK510 TRK510 TRK510 TR50S- reinforcing 12L 12L fibers Prepregmatrix Epoxy Epoxy Epoxy Epoxy Phenol Epoxy Epoxy Epoxy Epoxy Epoxyresin resin resin resin resin resin resin resin resin resin resinPrepreg resin 46.7 57.1 53.3 51.9 57.1 30.2 40.0 40.5 32.0 35.0 content(%) Substrate TR3110 TRK510 TR3110 TR3110 TR3110 Non- None H20 Non- Nonewoven woven fabric of fabric of nylon 12 polyester fiber fiber Prepreg0.85 1.1 0.71 0.96 1.1 0.18 0.73 0.74 0.62 0.19 thickness (mm) (A)Substrate 0.23 0.57 0.23 0.23 0.23 0.32 — 0.04 1.7 — thickness (mm) (B)(B)/(A) 0.27 0.52 0.32 0.24 0.21 1.78 — 0.05 2.74 — Pinholes and No NoNo No No No Yes Yes Yes Yes voids in FRP molded product TRK510: carbonfiber woven fabric Pyrofil TRK510, manufactured by Mitsubishi Rayon Co.,Ltd. TR3110: carbon fiber woven fabric Pyrofil TR3110, manufactured byMitsubishi Rayon Co., Ltd. WR800: roving glass cloth WR800, manufacturedby Nitto Boseki Co., Ltd., TR50S-12L: Unidirectional material comprisingcarbon fibers Pyrofil TR50S-12L, manufactured by Mitsubishi Rayon Co.,Ltd. H20: glass cloth H20 F5 104, manufactured by Unitika Glass FiberCo., Ltd.

INDUSTRIAL APPLICABILITY

The level of workability associated with conventional prepregs isretained, while a FRP with no internal voids or surface pinholes, andwith excellent external appearance, can be produced using molding usingonly vacuum pressure, without the use of an autoclave.

1. A prepreg comprising reinforcing fiber, a sheet-like reinforcingfiber substrate containing reinforcing fiber, and a matrix resin,wherein said matrix resin is impregnated into said sheet-likereinforcing fiber substrate and also covers one surface of saidsheet-like reinforcing fiber substrate, and a matrix resin impregnationratio is within a range of 35% to 95%.
 2. A prepreg comprisingreinforcing fiber, a sheet-like reinforcing fiber substrate containingreinforcing fiber, and a matrix resin, wherein said matrix resin existson both surfaces of said sheet-like reinforcing fiber substrate, and aportion inside said sheet-like reinforcing fiber substrate into whichsaid matrix resin has not been impregnated is continuous.
 3. A prepregcomprising a sheet-like reinforcing fiber substrate formed from areinforcing fiber woven fabric, and a matrix resin, wherein at least onesurface displays a sea-and-island-type pattern comprisingresin-impregnated portions (island portions) where said matrix resin ispresent at said surface, and fiber portions (sea portions) where saidmatrix resin is not present at said surface, a surface coverage ratio ofsaid matrix resin on surfaces with said sea-and-island-type pattern iswithin a range of 3% to 80%, and a weave intersection coverage ratio forsaid island portions, represented by a formula (1) shown below, is atleast 40%:Island portions weave intersection coverage ratio (%)=(T/Y)×100  (1)(wherein, T represents a number of island portions that cover weaveintersections, and Y represents a number of weave intersections withinsaid reinforcing fiber woven fabric on said surface with saidsea-and-island-type pattern).
 4. A prepreg according to any one of claim1 through claim 3, wherein said matrix resin is a thermosetting resincomposition.
 5. A prepreg according to claim 4, wherein saidthermosetting resin composition is curable by holding at 90° C. for 2hours.
 6. A prepreg according to claim 4, wherein a minimum viscosity ofsaid thermosetting resin composition is no more than 1000 poise.
 7. Aprepreg according to claim 4, wherein said thermosetting resincomposition comprises epoxy resin as a primary component.
 8. A prepregaccording to claim 4, wherein said thermosetting resin composition alsocontains a thermoplastic resin, and said thermoplastic resin is notdissolved within said thermosetting resin composition.
 9. A prepregaccording to claim 8, wherein said thermoplastic resin comprises shortfibers of thermoplastic resin with a length of 1 to 50 mm.
 10. A prepregaccording to claim 9, wherein said short fibers of thermoplastic resinhave a size of no more than 300 tex.
 11. A prepreg according to any oneof claim 1 through claim 3, wherein said reinforcing fibers are carbonfiber and/or glass fiber.
 12. A prepreg according to any one of claim 1through claim 3, wherein said sheet-like reinforcing fiber substrate hasa fiber weight within a range of 200 g/m² to 1500 g/m².
 13. A prepregaccording to any one of claim 1 through claim 3, wherein said sheet-likereinforcing fiber substrate is in a form selected from the groupconsisting of unidirectional materials, woven fabrics, knit fabrics,braided fabrics, mat materials, non-woven fabrics, and stitched sheets.14. A prepreg according to any one of claim 1 through claim 3, whereinsaid sheet-like reinforcing fiber substrate has a thickness of at least200 μm.
 15. A process for producing a prepreg, comprising the steps ofapplying a matrix resin on a resin support sheet, bonding a matrixresin-coated surface of said resin support sheet to both surfaces of asheet-like reinforcing, fiber substrate, and pressing a laminate of saidresin support sheets and said sheet-like reinforcing fiber substrateunder temperature conditions ranging from room temperature to 40° C. inorder to cause said matrix resin to impregnate said sheet-likereinforcing fiber substrate, thus forming a prepreg in which an interiorof said sheet-like reinforcing fiber substrate comprises a continuousportion that has not been impregnated with said matrix resin.
 16. Aprocess for producing a prepreg, comprising the steps of applying amatrix resin on a resin support sheet, bonding a matrix resin-coatedsurface of said resin support sheet to one surface of a reinforcingfiber woven fabric, bonding a protective film to another surface of saidreinforcing fiber woven fabric, subsequently applying heat and/orpressure in order to cause said matrix resin to impregnate saidreinforcing fiber woven fabric, thus forming a prepreg in which asurface of said reinforcing fiber woven fabric facing said protectivefilm displays a sea-and-island-pattern comprising resin-impregnatedportions (island portions) where said matrix resin is present at saidsurface and fiber portions (sea portions) where said matrix resin is notpresent at said surface.
 17. A process for producing a prepreg accordingto claim 16, wherein a thermosetting resin composition containing athermoplastic resin that is not dissolved within said thermosettingresin composition is also applied uniformly to said matrix resin-coatedsurface.
 18. An intermediate material for FRP molding comprising aprepreg containing reinforcing fibers and a matrix resin, and asubstrate containing essentially no impregnated thermosetting resincomposition, which is provided on at least one side surface of saidprepreg, wherein a ratio (B)/(A) between a thickness (A) of said prepregand a thickness (B) of said substrate is within a range of 0.1 to 2.5.19. A prepreg according to claim 18, wherein said matrix resin is athermosetting resin composition.
 20. An intermediate material for FRPmolding according to claim 18, wherein said substrate containingessentially no impregnated thermosetting resin composition contains afibrous thermoplastic resin.
 21. An intermediate material for FRPmolding according to claim 18, wherein said substrate containingessentially no impregnated thermosetting resin composition is anon-woven cloth of a thermoplastic resin.
 22. An intermediate materialfor FRP molding according to claim 18, wherein said substrate containingessentially no impregnated thermosetting resin composition containsreinforcing fibers.
 23. An intermediate material for FRP moldingaccording to claim 22, wherein said reinforcing fibers are identical tosaid reinforcing fibers incorporated within said prepreg.
 24. Anintermediate material for FRP molding according to claim 22, whereinsaid reinforcing fibers are positioned at a different angle to saidreinforcing fibers incorporated within said prepreg.
 25. An intermediatematerial for FRP molding according to claim 22, wherein said reinforcingfibers are different from said reinforcing fibers incorporated withinsaid prepreg.
 26. An intermediate material for FRP molding according toclaim 18, wherein said matrix resin is one of an epoxy resin compositionand a phenol resin composition.
 27. An intermediate material for FRPmolding according to claim 18, wherein said reinforcing fibersincorporated within said prepreg are carbon fiber and/or glass fiber.28. A process for producing an intermediate material for FRP molding,comprising the steps of preparing a prepreg using a lacquer-typeprocess, and bonding a substrate containing essentially no impregnatedthermosetting resin composition to at least one surface of said prepreg.29. A process for producing a fiber-reinforced composite material,comprising the steps of laminating a prepreg according to any one ofclaim 1 through claim 3, and conducting molding using vacuum bagmolding.
 30. A process for producing a fiber-reinforced compositematerial, comprising the steps of laminating an intermediate materialfor FRP molding according to claim 18, and conducting molding usingvacuum bag molding.
 31. A process for producing a fiber-reinforcedcomposite material, wherein prepregs according to any one of claim 1through claim 3 are laminated with identical side surfaces of saidprepregs facing to identical directions.
 32. A process for producing afiber-reinforced composite material, wherein an intermediate materialfor FRP molding according to claim 18 is laminated with identical sidesurfaces of said intermediate material facing to identical directions.33. A process for producing a fiber-reinforced composite materialaccording to claim 29, wherein in said vacuum bag molding process,primary curing is conducted for at least 10 minutes at a primary curingtemperature of no more than 150° C., and molding is then conducted at atemperature that is equal to, or greater than, said primary curingtemperature.
 34. A process for producing a fiber-reinforced compositematerial according to claim 31, wherein in said vacuum bag moldingprocess, primary curing is conducted for at least 10 minutes at aprimary curing temperature of no more than 150° C., and molding is thenconducted at a temperature that is equal to, or greater than, saidprimary curing temperature.
 35. A process for producing afiber-reinforced composite material according to claim 29, comprisingthe steps of deaerating said prepreg under conditions including atemperature within a range of room temperature to 50° C., and a pressureof no more than 50 Torr, and conducting molding by raising temperatureto a molding temperature, while said pressure is maintained at no morethan 50 Torr.
 36. A process for producing a fiber-reinforced compositematerial according to claim 35, wherein a rate of temperature increaseduring said raising of temperature to said molding temperature is set tono more than 1° C./minute when it starts from a point at least 20° C.below said molding temperature.